=Paper= {{Paper |id=Vol-2889/PAPER_14 |storemode=property |title=A Comprehensive Review on Digital Image Watermarking |pdfUrl=https://ceur-ws.org/Vol-2889/PAPER_14.pdf |volume=Vol-2889 |authors=Shweta Wadhera,Deepa Kamra,Ankit Rajpal,Aruna Jain,Vishal Jain }} ==A Comprehensive Review on Digital Image Watermarking== https://ceur-ws.org/Vol-2889/PAPER_14.pdf
A Comprehensive Review on Digital Image Watermarking
Shweta Wadheraa,b*, Deepa Kamrac, Ankit Rajpal d, Aruna Jaine and Vishal Jainf
a
  Department of Computer Science, Deen Dayal Upadhyaya College, University of Delhi, New Delhi, India
b
  Research Scholar, Sharda University, Greater Noida, India
c
  Department of Management Studies, Deen Dayal Upadhyaya College, University of Delhi, New Delhi, India
d
  Department of Computer Science, University of Delhi, New Delhi, India
e
  Department of Computer Science, Bharati College, University of Delhi, New Delhi, India
f
  School of Engineering and Technology, Department of Computer Science and Engineering, Sharda University
  Greater Noida, India


                Abstract
                The advent of the Internet led to the easy availability of digital data like images, audio, and video.
                Easy access to multimedia gives rise to the issues such as content authentication, security,
                copyright protection, and ownership identification. Here, we discuss the concept of digital image
                watermarking with a focus on the technique used in image watermark embedding and extraction
                of the watermark. The detailed classification along with the basic characteristics, namely visual
                imperceptibility, robustness, capacity, security of digital watermarking is also presented in this
                work. Further, we have also discussed the recent application areas of digital watermarking such
                as healthcare, remote education, electronic voting systems, and the military. The robustness is
                evaluated by examining the effect of image processing attacks on the signed content and the
                watermark recoverability. The authors believe that the comprehensive survey presented in this
                paper will help the new researchers to gather knowledge in this domain. Further, the comparative
                analysis can enkindle ideas to improve upon the already mentioned techniques.

                Keywords 1
                Digital Watermarking, Digital images, review, visual imperceptibility, robustness, copyright
                protection

1. Introduction
   In the present era, the secret to the success of an organization is all about the information it can gather.
Also, of concern is how effectively it can stop others from accessing the information generated through its
operations and processes. The popularity and availability of the Internet, easy access to digital storage
devices, have made the creation, replication, and distribution of digital media hassle-free. This has led to
the strong need of developing methods for preventing copyright breaches [1, 2].

   The technique of digital watermarking is being applied widely to the situations where an organization
wants to deter the data from spilling into the public domain. It is extremely crucial in cases where the
company is in direct fiduciary relationship with its customers and must protect their information as well
[1].



WCNC-2021: Workshop on Computer Networks & Communications, May 01, 2021, Chennai, India.
EMAIL: shweta.du@gmail.com (Shweta Wadhera)
ORCID: 0000-0002-3123-9976 (Shweta Wadhera)
           © 2021 Copyright for this paper by its authors.
           Use permitted under Creative Commons License Attribution 4.0 International (CC BY 4.0).
           CEUR Workshop Proceedings (CEUR-WS.org)


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   Digital Watermarking is a method to provide protection from any tampering or alteration [3, 4, 5]. It
provides security and authentication to digital content. The digital watermarking process involves the
insertion of signal, information into the original media content. The inserted information is then
uncovered and extracted to report the actual owner of the digital media.

   Watermarking involves embedding data called watermark or digital signature or label into the digital
media. This watermark can be extracted for revealing the authenticity of the media object [6]. As an
example of a watermark, we can imagine a visible “seal” over an image. A digital watermarking
algorithm has three basic parts: -

  1.    Watermark
  2.    The Encoding algorithm
  3.    The decoding algorithm [1, 7, 8].




Figure 1: The block diagram of Digital Watermarking Concept

   This technique may be used for copyright safeguarding and embedding fingerprints, placing
authentication for data integrity checks, and confidential communication. Another important application
of watermarking techniques includes tracing illegal users with an objective that the owner can approach
the regulatory authorities. It can be useful for ensuring that data pertaining to people who buy and sell
digital media, kept in record for each transaction. Further track of this data can be kept for controlling
copyright breaches. In fact, strict measures must be implemented for this unlawful distribution of digital
content.

    The paper is consolidated as follows: section 2 presents the classification of digital watermarking
based on various characteristics. Section 3 describes the prominent features of digital watermarking.
Section 4 covers the recent areas of application for watermarking. Section 5 presents the various types of
attacks. In section 6 we analyze the highlights and results of related work by various authors and section 7
presents the conclusions and future scope in the direction of image watermarking.

2. Classification of Digital Watermarking
    The section describes the classification of digital watermarking based on various criteria such as
robustness, perceptibility, domain, and detection process, multimedia. Further we also briefly present the
different popular watermarking techniques.



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2.1. Based on Characteristics/Robustness
Robust: Robust watermarking is preferred when copyright information is required to be inserted.
Robustness is indicated if the embedded watermark even after some attack is not damaged. It can
withstand several attacks. It is seen that for copyright protection, a robust watermark is advantageous.

Fragile: One can easily find out from the status of the watermark if the data has been altered. For
integrity protection, this watermark is preferred.

Semi-fragile: Some extent of change is tolerated by a semi-fragile watermark [2, 3, 6].

2.2. Based on Perceptibility
Perceptible: A watermark that is visible is known as perceptible.

Imperceptible: Incase the watermark is invisible then it is known as imperceptible watermark. In this,
information which is embedded into the image is not visible. In such cases one can prove the ownership
of your image with the help of imperceptible watermark [2, 26].

2.3. Based on Domain
Frequency domain: First, the transforming of the image to the frequency domain is carried out. In this
type of watermarking different transformation techniques are applied such as DCT, DFT, and DWT [27].

Spatial Domain: Watermarking in this domain moderately changes the value of pixels, of arbitrarily
selected portions of images; the watermark is inserted in the host image. No conversion or transformation
is applied in the spatial domain. LSB, Patchwork method, SSM Modulation are some of the popular
spatial domain-based techniques [2, 3].

   Generally, the watermarking carried out in the frequency domain is more robust as compared to the
one carried out in the spatial domain.

2.3.1. Spatial Domain
Least Significant bit (LSB) method

    In this method, the watermark is inserted in the least significant bit (LSB of image pixels. Ideally,
either of two ways is used for embedding. In one approach, the LSB of an image is substituted with a
pseudo-noise (PN) sequence, while another approach adds this PN sequence to the LSB. LSB technique
provides ease of use but compromises on the robustness parameter against attacks.

Patchwork Method

    Patchwork method randomly picks n pairs of image points (x, y). The data in the x region is lightened
and data in the y region is darkened. However, this technique can withstand a series of attacks, but it lacks
in terms of capacity.




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Figure 2: Classification of Digital watermarking

2.3.1. Frequency Domain
Discrete cosine transforms (DCT)

   This method employs a technique of subdividing an image signal into non-overlapping blocks of 8 × 8
size. Further, block-wise DCT is performed, and thereafter the choice of coefficients to be watermarked is
carried out. Finally, an inverse DCT is applied on each 8 × 8 block to obtain the signed image.

Discrete wavelets transform (DWT)

    In this method, the image is subjected to a sequence of low-pass and high-pass filters. An image is
decomposed into four equal sub-bands where each sub-band comprises low frequency (LL), horizontal
features (LH), vertical features (HL), and diagonal features (HH). It is a preferred algorithm as it provides
a robust and secure watermarking method [2, 3, 27].




Figure 3: Three level decomposition in 2D DWT


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2.4. Based on Detection process

  Blind: Those watermarking processes fall in this category wherein the removal of the embedded
   information requires only the watermarked image. Its applications can be copyright protection, e-
   voting, etc. [9].

  Non-Blind: In this type of watermarking, the process copies along with the text data, the host image,
   and the inserted information for the retrieval of the watermark. Its application is seen in copyright
   protection [9].

2.5. Based on Multimedia

  Text Watermarking: It consists of components like words, punctuations, sentences, etc.
   Transformation is done on one of these components and is embedded as a watermark [3].

  Image Watermarking: Large-size images are there which has to be watermarked. In the case of
   images, we require robust watermarks, which should be imperceptible [3].

  Video watermarking: In this case, it is difficult to get imperceptible watermark.

  Graphic Watermarking: In 2D or 3D digital graphics, a watermark is embedded. It provides
   copyright protection.

3. Basic Characteristics of Digital Watermarking
Mentioned here are various features of Digital Watermarking.

  Robustness: The robustness feature indicates that the digital watermark can resist various processing
   operations and attacks. Then it is considered to be robust [14].

  Imperceptibility: The imperceptibility feature indicates that a digital watermark should not be seen
   by the human eye. One should not be able to see the embedded watermark. It can only be identified
   by specialized procedures. The watermark should be such that the viewer should not be able to see it
   and the process of embedding a watermark should be such that the quality of the content is
   maintained [14].

  Security: The security feature indicates that irrespective of targeted attacks, the inserted digital
   watermark cannot be removed. Watermark security describes that altering or removing a watermark
   without any deterioration to the host signal should be arduous. Watermarking security can be
   explained as a way to provide secrecy, ownership, and protection of data [2].

  Capacity: The amount of information embedded in a watermarked image also known as data
   payload [3].




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Figure 4: Basic Characteristics

  Verifiability: Through the watermark, we should be able to get a piece of evidence regarding the
   ownership of copyright-protected data. This helps in verifying the authenticity of any digital data and
   even the control of its unlawful copying [29].

4. Recent Applications of Watermarking

  Copyright protection: As we are aware that images can be easily circulated and are freely available
   over the internet. These images can be used commercially. So copyright protection of data is needed
   and for this Digital Watermarking is very useful. The inserted digital watermark will be used to
   identify the copyright owner [2, 9].

  Fingerprint: Fingerprinting in digital watermarking can be put up as a method for embedding some
   distinctiveness. The fingerprint should be difficult to alter. The information inserted is related to the
   customer. It is through this fingerprinting that it is revealed about those authorized customers who
   are involved in the circulation of copyright data by breaching the agreement [2, 27].




Figure 5: Applications of Digital Watermarking

  Copy control: Digital watermarking can prevent illegal duplication of digital data. Devices that do
   replication can detect these watermarks and report copying and thereby put a control on illegal
   copying [3, 26].

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  Broadcast Monitoring: Over the years it has been seen that availability and accessibility to media
   content have increased exponentially. Also, the content is available through the internet. In such
   times, it has become important for content owners and copyright owners to know about the real
   distributor of content. Digital Watermarking has an important role here [3, 26].

  Medical Application: Embedding of patient name in the MRI-scan, CT-scan or X-ray reports can be
   done using visible watermarking. The treatment of the patient depends on these medical reports. So
   to avoid mixing of reports the technique of visible watermarking can be used [9].

  Electronic Voting System: The Internet has spread all over the country from big towns to small
   villages. Electronic voting helps to carry out elections, keeping the security aspect into consideration
   [9].

  Remote Education: Lack of teachers poses a big problem in small villages. Smart Technology
   needs to be adopted for distance learning. In this case watermarking plays its role in the authentic
   transmission of study material over the internet [9, 27].

5. Attacks on Watermarking
    A digital Watermarking scheme is always assessed by the fact that how robust it is over attacks.
Attack on any watermark is used to harm the inserted watermark or enfeeble the watermark's discovery.
Hampering the protection, which a watermark provides to digital content, is the objective of any attack.
Watermarking attacks can be classified as follows – Geometry attack, Protocol attack, Cryptographic
attack, and removal attack [10, 11, 12].

  Geometry Attack: Such processing is done over the watermark image which alters the geometry of
   the image like rotation, cropping, etc. These can be further classified into – scaling, cropping,
   rotation, and translation [6].
  Removal Attack: This attack aims at removing the inserted data from the digital image. If it is not
   able to, yet they try to destroy the embedded information [29].




 Figure 6: Types of Attacks on Digital Watermarking

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  Protocol Attack: The attacks which come under this category, do not damage the embedded data.
   Two types of Protocol attacks are there: Invertible, Copy attack. So a watermark should be non-
   invertible and should not be copied. A watermark is invertible when the attacker removes his own
   watermark from the host data. The attacker then pretends to be the owner of the data. This shows that
   for copyright protection, watermarks should be non-invertible [13, 29].

  Copy Attack: It is also a form of Protocol attack. In this also the watermark is not destroyed.
   Instead, the attacker estimates the watermark from host data. It is then copied to other data [13].

  Cryptographic Attack: These types of attacks include those which break the security in
   watermarking techniques. With this, they can extract the inserted watermark data or can insert some
   delusive watermark. The Brute-force and Oracle attacks fall under this category [29].
   In order to present an exhaustive survey on image watermarking, we created a repository of more than
50 papers on Mendeley and 35 papers were used to develop the background of digital watermarking and
19 papers were found relevant in the area of image watermarking.

   Table 1 summarizes the watermarking schemes proposed by various research groups in the past few
years through the comparative analysis.

Table 1: Comprehensive survey of recent image watermarking schemes
Research          Title      Technique used        Input          Visual               Robustness
group                                                             Imperceptibility
Abraham “An                  Spatial domain        Cover image PSNR =                  NCC = Range
and Paul imperceptible       Simple Image          Colored        47.6 dB              [0.9917 – 1]
[6]        spatial domain    Region Detector       image of
           color image       (SIRD): Estimation    Size:          SSIM =               BER= Range
           watermarking      of most suitable      512 x 512 x 3 0.9904                [0.7500-0]
           scheme”           portion within the    pixels
                             block of an image.                                        Attacks
                                                   Watermark                           considered:
                                                   Size:
                                                   64 x 64 pixels                      Salt and
                                                                                       Pepper,
                                                                                       Poisson,
                                                                                       Speckle,
                                                                                       average
                                                                                       filtering,
                                                                                       Gaussian LPF,
                                                                                       Sharpening,
                                                                                       JPEG
                                                                                       Compression,
                                                                                       Cropping,
                                                                                       Resizing
Liu et al.   “Secure and      Scrambling             Cover image     PSNR              NCC Range
[7]          robust digital   Watermark: RSA         Colored         Range =           =[0.6053 -
             image            Encryption             Size: 512 x     [38.68 -48.03]    0.9673]
             watermarking                            512 pixels      dB
             scheme using     DWT + SVD Hybrid                                         Attacks

                                                 133
             logistic and RSA                          Watermark                        Considered:
             encryption”        Different              Size: 256 x
                                embedding strength     256 pixels                       Mean
                                is used.                                                Filtering,
                                                                                        Median
                                                                                        Filtering,
                                                                                        Gaussian
                                                                                        Noise,
                                                                                        Salt & Pepper
                                                                                        Noise,
                                                                                        Rotation,
                                                                                        Crop,
                                                                                        JPEG
                                                                                        compression
Vaidya                          DWT-CT-Schur-SVD       Cover image    Watermark1        NCC=1.0
and          “A robust semi-                           Colored
Mouli        blind              Discrete Wavelet                      PSNR range =
[14]         watermarking       Transform (DWT):       Two            [27.63-36.16]     Attacks
             for color images   1-level                Watermarks dB                    Considered:
             based on           decomposition          of Size:                         Salt & Pepper,
             multiple           Contour Let            64 x 64 pixels SSIM range =      Gaussian
             decompositions     Transform (CT): 2-                    [0.9709-          Noise,
             ”                  level on LL subband                   0.9989]
                                to obtain 𝐷 .
                                Schur Transform:                      Watermark2
                                𝐷 is decomposed
                                as 𝐷 =                                PSNR Range
                                𝑄 . 𝑃 . [𝑄 ]                          =[22.38- 31.59]
                                Singular Value                        dB
                                Decomposition
                                (SVD): Watermark
                                is inserted in 𝑃 .
Liu et al.   “Digital image                            Cover image    PSNR              Attacks
[15]         watermarking       Fractal encoding       Size:          Range=[41-45 ]    Considered:
             method based       and DCT method         1024 x 1024    dB                white noise
             on DCT and         are combined for       pixels                           attack,
             fractal            double encryption                                       Gaussian filter
             encoding“          for embedding          Watermark                        attack, JPEG
                                purpose.               Size:                            compression
                                                       256 x 256                        attack.
                                                       pixels



Savakar   “Robust               Secret key: Select     Cover Image    PSNR =            NCC=
and Ghuli Invisible Digital     the place of           Plenoptic      Range[51.68-      Range[0.9139-
[16]      Image                 insertion of the       Size:          64.54] dB         1.0]


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            Watermarking     logo.                   512 x 512
            Using Hybrid                             pixels           SSIM=
            Scheme”          DCT + SVD Hybrid                         Range[0.9989-     Attacks
                                                     Watermark        1.0000 ]          Considered :
                                                     Binary
                                                     Size:                              Gaussian
                                                     50 x 20 pixels                     Noise,
                                                                                        Speckle noise,
                                                                                        Salt and
                                                                                        pepper noise,
                                                                                        Poisson Noise,
                                                                                        Rotation,
                                                                                        JPEG
                                                                                        Compression

Moosaza     “A new DCT-      Image                   Cover image      PSNR=             NCC =
deh and     based robust     watermarking            Size:            Range[39.95-      Range
Ekbatanif   image            scheme based on         512 x 512        40.73]            [0.7871-
ard [17]    watermarking     DCT                     pixels                             0.9901]
            method using
            teaching-        Teaching-Learning-      Watermark
            learning-Based   Based Optimization      Size:                              Attacks
            optimization”    (TLBO): Automatic       32 x 32 pixels                     considered :
                             detection of
                             embedding                                                  Salt & pepper
                             parameters and                                             noise,
                             suitable position for                                      Uniform
                             inserting the                                              noise, Poisson
                             watermark.                                                 noise,
                                                                                        Gaussian
                                                                                        noise, Scaling,
                                                                                        Rotation,
                                                                                        Cropping,
                                                                                        Sharpening,
                                                                                        Motion Filter,
                                                                                        Disk filter,
                                                                                        Wiener,
                                                                                        Median filter,
                                                                                        Gaussian
                                                                                        Filter, JPEG
                                                                                        compression

Su et al.   “Improved        Watermark bits are      Cover image      PSNR =            NCC=
[18]        wavelet-based    embedded in the         Colored          Range [37.6262-   Range
            image            spatial domain on       Size:            38.0535]          [0.8413-
            watermarking     DC coefficients         512 x 512                          1.0000]
            through SPIHT”   using 2D-DFT.           pixels
                                                                      SSIM=

                                                  135
                                                     Watermark     Range[0.9231-
                                                     Size:         0.9414]
                                                     32 x 32
                                                     pixels
           “Improved         DWT + DCT + SVD         Cover image   PSNR=            NCC=
Kumar et   wavelet-based     Set Partitioning in     Size:         Range            Range
al. [19]   image             Hierarchical Tree       512 × 512     [25.31- 38.47]   [0.9422-
           watermarking      (SPIHT) and Arnold      pixels                         0.9990 ]
           through SPIHT”    transform for                         SSIM=
                             enhancing               Watermark     Range            Attacks
                             robustness.             Size:         [0.971311-       Considered
                                                     256× 256      0.999954 ]
                                                     pixels                         Salt & Pepper,
                                                                                    Gaussian
                                                                                    Noise, JPEG
                                                                                    compression,
                                                                                    cropping,
                                                                                    Rotation,
                                                                                    Scaling
                                                                                    attacks,
                                                                                    Sharpening
                                                                                    Mask, Median
                                                                                    Filter,
                                                                                    Histogram

Kahlesse   “A robust blind   LSB substitution        Cover Image   PSNR > 40 dB     NCC=
nane       color image       method is used.         Colored                        Range[0.6437-
Fares et   watermarking      Watermark is            Size:                          0.98265]
al. [20]   based on          embedded within         512 x 512
           Fourier           the mid-band            Pixels                         Attacks
           transform         coefficients and                                       considered
           domain”           frequency
                             components.             Watermark                      Gaussian
                                                     Size:                          noise,
                                                     random                         Gaussian
                                                     sequence of                    filter,
                                                     45,000 bits                    Histogram,
                                                                                    JPEG,
                                                                                    rescaling,
                                                                                    Rotation,
                                                                                    cropping,
                                                                                    Gaussian
                                                                                    noise, Image
                                                                                    sharpening,
                                                                                    Blurring,
                                                                                    rotation, JPEG
                                                                                    compression,
                                                                                    salt & Pepper

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                                                                                    noise, Median
                                                                                    filter,
                                                                                    cropping,
                                                                                    Rotation

Yuan et     “New image        Blind watermarking    Cover Image    Watermark1       NCC =
al. [21]    blind             method:               Colored                         Range [0.9997
            watermarking      Two dimensional       Size:          PSNR =           – 1]
            method based      DCT is performed      512 × 512      range[36.3189-
            on two-           on selected blocks.   Pixels         38.2472]         Attacks
            dimensional       Middle frequency                     SSIM= range      considered :
            discrete cosine   coefficients are      Two Colored    [0.9149 -
            transform”        embedded.             watermarks     0.9441]          JPEG(40),
                                                    Size:                           JPEG 2000,
                                                    32 × 32                         Gaussian
                                                    Pixels         Watermark2       white Noise,
                                                                                    salt & pepper
                                                                   PSNR =           Noise, Butter
                                                                   Range            worth low-
                                                                   [36.1885 –       pass filtering,
                                                                   38.4066 ]        Median
                                                                                    filtering,
                                                                   SSIM =           cropping
                                                                   Range
                                                                   [0.9154 –
                                                                   0.9724 ]
Anand       “An improved      Medical image         Cover image    PSNR =           NCC=
and         DWT-SVD           watermarking in       MRI image of   Range            [0.9724 -
Singh       domain            DWT-SVD domain.       Size:          [32.6229 -       0.9873]
[22]        watermarking      Hamming code is       512 x 512      34.0455]
            for medical       put to text           Pixels                          Attacks
            information       watermark before                                      considered :
            Security”         embedding.            Watermark      SSIM=
                              Chaotic-LZW and       Size:          Range            Salt & Pepper
                              hyper Chaotic -LZW    256 x 256      [0.9950 -        noise,
                              are used.             Pixels         0.9955]          Gaussian
                                                                                    noise,
                                                                                    Rotation, JPEG
                                                                                    compression,
                                                                                    Speckle noise,
                                                                                    Cropping,
                                                                                    Median filter,
                                                                                    Histogram
                                                                                    equalization

Mishra et   “Bi-directional   DWT-BELM              Cover image    PSNR=            NCC=
al. [23]    extreme           approach              JPEG           Range[42.49-     Range[0.95-
            learning          DWT: 4-level          compressed     42.67] dB        1.00]

                                                137
            machine for       Bi-directional ELM      image
            semi-blind        (B-ELM): Variant of     Size:            SSIM=            BER=
            watermarking of   ELM is modeled          512 x 512        Range            Range
            compressed        with LL4                Pixels           [0.9960 -        [0.0938 -
            images”           coefficients for                         0.9969]          0.1074 ]
                              Semi-blind              Watermark
                              recovery.               Binary                            Attacks
                                                      Size:                             considered :
                                                      32 x 32 Pixels
                                                                                        Low pass
                                                                                        Gaussian
                                                                                        filter, Median
                                                                                        filter,
                                                                                        Gaussian
                                                                                        noise, Salt &
                                                                                        Pepper noise,
                                                                                        Rotation,
                                                                                        Scaling,
                                                                                        Cropping

Ambadek     “Digital Image    DWT and                 Cover Image      PSNR=            NCC=
ar et al.   Watermarking      encryption-based        Size:            54.96 dB         0.9749
[24]        Through           watermarking.           228 × 228
            Encryption and                            Pixels                            Attacks
            DWT for                                                                     Considered :
            Copyright                                 Watermark
            Protection”                               Size:                             Noise,
                                                      grayscale                         Geometric,
                                                      image                             Compression
                                                      90 × 90
                                                      pixels
Su et al.   “An               Spatial domain          Cover Image      PSNR =           NCC =
[30]        Approximate       watermarking using      Size:            Range[40.0691-   Range[0.9912-
            Schur             Schur                   512 x 512        40.6450] dB      1.0]
            Decomposition-    Decomposition           Pixels
            based Spatial     Maximum
            Domain Color      eigenvalues are         Watermark        SSIM =           Attacks
            Image             approximated and        Size:            [0.9594-         Considered :
            Watermarking      used for embedding      32 x 32          0.9681]          Rotation, JPEG
            Method”           and blind               Pixels                            (30), JPEG
                              extraction.                                               2000, Salt &
                                                                                        Peppers noise,
                                                                                        Gaussian
                                                                                        Noise, Median
                                                                                        filtering,
                                                                                        Butterworth
                                                                                        lowpass
                                                                                        filtering,

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                                                                                           Sharpening,
                                                                                           Blurring,
                                                                                           Scaling,
                                                                                           Cropping
Rajpal et   “Multiple          4-level DWT              Cover Image      PSNR = [42-43]    BER <=0.0029
al. [31]    scaling factors    decomposition is         Size:            dB
            based Semi-        used.                    512 x 512                          Attacks
            Blind              LL4 coefficients are     Pixels                             Considered :
            Watermarking       embedded with                                               JPEG
            of Grayscale       multiple scaling         Watermark                          Compression,
            Images using       factors.                 Size:                              Rotation,
            OS-ELM             OS-ELM is used for       32 x 32 Pixels                     Gaussian
            Neural             semi-blind                                                  noise, Salt &
            Network”           watermarking.                                               Pepper



Hosny et    “Parallel Multi-   Moments of the           Cover Image      PSNR=             NCC=
al. [32]    Core CPU and       polar complex            Size:            Range [40.597 –   For colored
            GPU for Fast       exponential              Colour           53.64 ] dB        images
            and                transform obtained       images and                         Range
            Robust Medical     using Simplified         grayscale                          [0.9100 – 1.0]
            Image              exact kernels are        medical
            Watermarking”      used for the             images                             For Grayscale
                               restoration of           256 x 256        SSIM=             images
                               watermark.               Pixels           Range [0.933 –    Range
                                                                         0.980]            [0.9358 – 1.0]
                                                        Watermark
                                                        Size:                              BER=
                                                        32 x 32                            For colored
                                                        Pixels                             images
                                                                                           Range
                                                                                           [0 – 0.0156]

                                                                                           For Grayscale
                                                                                           images
                                                                                           Range
                                                                                           [0 – 0.0176]

                                                                                           Attacks
                                                                                           Considered :
                                                                                           Rotation at
                                                                                           various
                                                                                           angles, Scaling
                                                                                           factor,
                                                                                           Translation,
                                                                                           Scaling +
                                                                                           Rotation,

                                                      139
                                                                                      Scaling + JPEG
                                                                                      compression,
                                                                                      Rotation +
                                                                                      JPEG
                                                                                      compression,
                                                                                      JPEG
                                                                                      compression,
                                                                                      Salt & Pepper
                                                                                      Noise,
                                                                                      Gaussian
                                                                                      Noise,
                                                                                      Gaussian
                                                                                      filtering,
                                                                                      Median
                                                                                      filtering

Taha et     “Adaptive Image   Integer-based lifting   Cover Image   PSNR=             NCC=
al. [33]    Watermarking      wavelet transform       Size:         Range [32.3236    Range
            Algorithm Based   is used.                512 x 512     – 40.5670] dB     [0.7798 – 1]
            on an Efficient                           Pixels
            Perceptual
            Mapping                                                 SSIM=
            Model”                                    Watermark     Range
                                                      Size:         [0.9522 –         BER=
                                                      Binary        0.9883]           [0 – 0.1914]
                                                      32 x 32
                                                      Pixels                          Attacks
                                                                                      Considered :
                                                                                      JPEG
                                                                                      compression,
                                                                                      Salt & Pepper,
                                                                                      Gaussian
                                                                                      Noise,
                                                                                      Sharpen,
                                                                                      Median Filter,
                                                                                      Average filter,
                                                                                      Rotate, Scale
                                                                                      Down, Crop


Rajpal et   “Fast Digital     Generation of           Cover Image   PSNR = [39.70-    NCC = [0.71-
al. [34]    Watermarking      watermark               Colored       45.72]            0.99]
            of                sequence using DCT      Size:
            Uncompressed      using host image        256 x 256
            Colored Images                            Pixels        SSIM = [0.9965-   Attacks
            using             Informed                              0.9991]           Considered :
            Bidirectional     watermarking using
            Extreme           Extreme Learning                                        Low pass

                                                  140
              Learning         Machine (ELM) and      Watermark                         Filter,
              Machine”         Bi-directional ELM     Size:                             Gaussian
                               (B-ELM)                1024 x 1024                       Noise, Scaling,
                                                      Pixels                            Crop, JPEG
                                                                                        compression

Alshoura      “A New Chaotic   IWT-SVD Hybrid is      Cover image    PSNR=              NCC=
et al. [35]   Image            used.                  Size :         Range [46.85 –     Range
              Watermarking     Random key is          512 x 512      52.33] dB          [0.99101-
              Scheme Based     generated using        Pixels                            0.99513]
              on SVD and       cover image and the
              IWT”             watermark image.                                         Attacks
                               This key is utilized   Watermark                         Considered :
                               for embedding of       Grayscale                         Cropping,
                               watermark using        image                             Cutting,
                               chaotic multiple       Size:                             Translating,
                               scaling factors        256 x 256                         Shifting,
                               (CMSF).                Pixels                            Rotating,
                                                                                        Scaling,
                                                                                        Median filter,
                                                                                        Gamma
                                                                                        Correction,
                                                                                        Median filter,
                                                                                        Wiener filter,
                                                                                        Histogram
                                                                                        equalization,
                                                                                        Salt Peppers
                                                                                        Noise,
                                                                                        Speckle
                                                                                        Noise,
                                                                                        Gaussian
                                                                                        Filter, JPEG
                                                                                        Compression

   In Table 1, a study and evaluation of work done in digital watermarking techniques in past are
enumerated. The spatial domain and frequency domain techniques are some popular techniques examined
in the past. Also, it has been observed that the spatial domain digital watermarking technique is less
robust and hence less preferred. The performance of the watermarked image is evaluated through
robustness, imperceptibility, security, and capacity. Among these the most preferred criteria, were the
visual imperceptibility of the watermarked image and the robustness of the watermarking. In fact, the
future work holds scope by combining techniques and using them in hybrid form to not only enhances the
robustness of the watermarked image, but it may also reduce the drawbacks of each method considered
separately.

6. Conclusions
   This paper gives an overview of techniques of digital image watermarking along with the detailed
classification and characteristics. The various application areas such as medical, remote education,
military, electronic voting systems have been presented. It has been seen that data security has become a
top priority due to the extensive transmission of digital data. So, for providing authorized data or

                                                  141
safeguarding important data, digital watermarking is used. The performance of the watermarked images is
evaluated through robustness, imperceptibility, security, and capacity. These are analyzed using peak
signal to noise ratio and bit-error ratio. It was observed that robustness was a preferred criterion. Invisible
watermarking is carried out for content authentication and proof of ownership. Research groups have
preferred frequency domain techniques and have tried to work on balancing between robustness and
visual imperceptibility. Through the paper, we analyze various watermarking methods in digital images
used in the recent past.

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