2. Introduction
Image authentication techniques have become very important due to
the emergence of wide range multimedia applications.
Images have to cross non-secure channels like the Internet for
transmission.
Images must be protected against manipulation attempts, especially
in the case of military and medical applications.
Unauthorized replication is also a problem, which leads copyright
dispute for actual ownership.
3. Image Authentication
A mechanism to ensure
The image is not faked
The image is originated from a trusted sender
Authentication
Data Authentication (Content protection)
Owner authentication
4. Digital Watermarking
Digital Image Watermarking is a technique for inserting
information (the watermark) into an image, which can
be later extracted or detected for protecting digital
content copyright and ensuring tamper-resistance, which
is hard to remove by unauthorized persons.
5. Digital Watermarking Process
A watermarking system is
usually divided into three
distinct steps.
• Embedding
• Attack
• Detection
6. • Embedding F : Watermarked Image = Function (Cover, Watermark, Key)
• Extraction F : Watermark = Function (Watermarked Image, Cover, Key(
• Non-blinded detection: Original host image(Cover) is used in detection part.
• Blinded detection: When Cover is not used in detection part.
Digital Watermarking Process
(Non-blinded and with key)
7. Embedding
In embedding, an algorithm accepts the host and the data to be
embedded, and produces a watermarked signal.
• Inputs to the scheme are the watermark, the cover data and an
optional public or secret key. The output are watermarked data.
The key is used to enforce security.
• Image Content
Spatial Domain (Ex-Least Significant Bit Watermarking)
FFT - Magnitude and Phase
Wavelet Transforms
DCT Coefficients
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8. Extraction/Detection
Detection (often called extraction) is an algorithm which is applied to
the attacked signal to attempt to extract the watermark from it. If the
signal was unmodified during transmission, then the watermark still is
present and it may be extracted.
Inputs to the scheme are the watermarked data, the secret or public
key and, depending on the method, the original data and/or the
original watermark.
The output is the recovered watermarked W or some kind of
confidence measure indicating how likely it is for the given
watermark at the input to be present in the data under inspection.
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9. Watermark Detection
* =
Suspected Image
Extracted
Watermark,W2
Original
Watermark,W1
Correlation
•Watermark Extracted from Suspected Image
•Correlation, =E[W1*W2]/{ E[W12]E[W22]}
•Compute correlation of Extracted and Original Watermark
•Threshold correlation to determine watermark existence
10. Attacks on Watermarking
Unintentional
All image manipulations commonly used to prepare images for print
publication.
For example: Resizing, rotation, sharpening, contrast modification,
compression, etc.
Intentional (Malicious)
All the well-known intentional attacks include: Disabling, altering,
embedding new watermark etc.
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12. SVD Domain Watermarking
[U1,S1,V1] = svd(A); // A is cover image
temp = S1+(a * W); // a is scaling factor, and W is watermark
[Uw,Sw,Vw] = svd(temp);
Aw = U1*Sw*(V1.'); // Aw is watermarked image
Extraction of watermark in SVD domain
[Uw1,Sw1,Vw1] = svd(Aw);
D = Uw*Sw1*(Vw.') //temp;
W = (D-S1)/a;
13.
14.
15.
16.
17. Watermark Properties
Watermark should appear random, noise-like
sequence
Appear Undetectable
Good Correlation Properties
High correlation with signals similar to watermark
Low correlation with other watermarks or random
noise
W=[1 0 0 1 0
0 1 1 0 1
1 1 0 1 0
0 1 1 1 1
0 1 0 0 0]
18. Steganography vs. Watermarking
Steganography is to hide a message m in data d such eavesdropper cannot
detect the presence of m in d.
Watermarking is to hide a message m in data d, to obtain new data s0 an
eavesdropper cannot remove or replace m in d.
Main aim of Steganography is imperceptibility of human senses, whereas main
aim of watermarking is robustness.
19. Cryptography vs. Watermarking
Cryptography is the most common method of protecting digital content and is
one of the best developed science.
However, encryption cannot help the seller monitor how a legitimate
customer handles the content after decryption.
Digital watermarking can protect content even after it is decrypted.
21. Classifications of digital watermarking
o Robust watermark
It sticks to document ( image, audio, video or text) to which it is embedded.
Removing it destroys the quality of signal.
It is used for copyright protection.
Frequency based techniques are very robust against attack involving image compression
and filtering because the watermark is actually spread through the image.
As high frequency component is not resistant to JPEG compression so low frequency
component are used for watermarked embedding.
o Fragile Watermark
It breaks very easily on modifying host signal.
It is used for temper detection, finger printing and digital signature.
Hash code of the host image can be used as fragile watermark for tamper detection.
o Semi Fragile Watermark
It is sensitive to signal modification and gives information about nature and location of
attack also, it provides data authentication.
22. Limitations / Conclusions
Rapidly growing field of digitized images, video and audio has
urged for the need of protection.
Watermarking is a key process in the protection of copyright
ownership of electronic data (image, videos, audio, ...).
Digital watermarking does not prevent copying or distribution.
Digital watermarking alone is not a complete solution for
access/copy control or copyright protection.
Digital watermarks cannot survive every possible attack.22
23. References
1. Mohmmad Ali M. Saiyyad, Nitin N. Patil (2014). Authentication and Tamper
Detection in Images Using Dual Watermarking Approach IEEE
2. Qingtang Su, Gang Wang, Xiaofeng Zhang, Gaohuan,Beijing Chen (2017). A
new algorithm of blind color image watermarking based on LU decomposition
Multidim Syst Sign Process, Springer
3. Wikipedia article on Digital watermarking