1. Digital Forensics 2 Lecture 4:Watermarking Presented by : J.Silaa
Lecturer: FCI
19 Sept 2017

2. Objectives Watermarking history Information hiding and watermarking
Types of Digital Watermarks
Common applications of Watermarks
Watermarks attacks

4. Formal definitions
• Cryptography: It is the study of methods of sending messages in
distinct form so that only the intended recipients can remove the
disguise and read the message.
• Steganography: It hides messages in plain sight rather than
encrypting the message. The message is embedded in the data
(that has to be protected) and does not require secret transmission.
• Watermarking: It is the process that embeds data called a
watermark, tag, or label into a multimedia object such that
watermark can be detected or extracted later to make an assertion
about the object. The object may be an image or audio or video or
text. ( Chen,2005)
Steganography main goal:
to hide message M in some audio/video/text cover data D to obtain a new data D’ practically
Indistinguishable from D by people ,in such a way that an eavesdropper cannot detect the presence of M in D’
Watermarking main goal:
Indistinguishable from D by people ,in such a way that an eavesdropper cannot remove or replace M in D’

5. Information Hiding : Watermarking
The use of watermarks is almost as old as paper manufacturing
In more recent times, watermarks have been used to certify the composition of paper, including the nature of the fibers used.
• Today most developed countries also watermark
their paper, currencies, and postage stamps to
make forgery more difficult.

6. Watermarking process
Watermarks are embedded directly into a file data, usually by making minor variations to pixel brightness.
Watermarks are not text that is included in the file description "Comments" field.
The variations in the data bits are subtle and cannot be detected by the human eye. The patterns are repeated many times, allowing the information contained in the watermark to be recovered even if the image is cropped.
Some watermarks can survive a limited amount of image manipulation, such as contrast adjustments and filtering
Common Watermarking Techniques includes
Time domain –LSB Modifications
Frequency Domain
Wavelength Domain
Video watermarking algorithms are DFT,DCT,DWT
DFT=Discrete Fourier Transform, DCT=Discrete Cosine Transformation, DWT= Discrete Wavelet Transformation
For more download and read

7. Types of Digital Watermarks
Based on the type of document to be watermarked:
Image Watermarking
Video Watermarking
Audio Watermarking
Text Watermarking

8. Types of Digital Watermarks
Based on the human perception:
Visible Watermark
Invisible-Robust Watermark
Invisible-Fragile Watermark
Dual Watermarking
Robust: Is a type of watermark difficult to remove
Fragile : Is destroyed if anybody try to temper with the image.
Fragile watermarking fails to detect after slight modifications

9. Common applications of Watermarks
Currently, watermarking is used for
Copyright protection - to prevent identity theft third parties from claiming the ownership of the digital media.
Fingerprinting - to convey information about the
recipient of the digital media (rather than the
owner) in order to track distributed copies of the
media.
Copy protection - to control data copying devices and prevent them from copying the digital media if the media is copy-protected.
Image authentication - to check the authenticity of the digital media.
Watermarking Photos on eBay
eBay has a strict recommendations with some restrictions for watermark on selling item’s photos.
Image Watermark Studio is a perfect free tool for eBay sellers to do this.
If you plan to sell items on eBay auction site, you must have to read this tutorial (

10. Visible Watermark and Its Applications
Visible watermark is a secondary
translucent overlaid into the primary image
The watermark appears visible to
a casual viewer on a careful inspection.
Applications:
– Enhance copyright protection
– Indicate ownership originals

11. Visible Watermark and Its Applications

12. Desired Characteristics of Visible Watermarks
Obvious in both color and monochrome images
Spread in a large or important area of the image
in order to prevent its deletion by clipping.
Visible yet must not significantly obscure the
image details beneath it.
Difficult to remove.
Can be applied automatically with little human
intervention and labor.

13. Invisible-Robust Watermark and Its Applications
Invisible-robust watermark is embedded in
such a way that alterations made to the
pixel value is perceptually not noticed and
it can be recovered only with appropriate
decoding mechanism.
Applications:
Detect misappropriated images
Show the evidence of ownership

14. Invisible watermarks

15. Desired Characteristics of Invisible Robust Watermarks
It should neither be noticeable to the viewer nor
should degrade the quality of the content.
It must be robust to common signal distortions and
must be resistant to various intentional tampering’s
solely intended to remove the watermark.
Retrieval of watermark should unambiguously
identify the owner.
It is desirable to design a watermark whose decoder is scalable with each generation of computer.

16. ..Desired Characteristics of Invisible Robust Watermarks
The amount of pixel modification should be
minimum.
Insertion of watermark should require little human
intervention or labor.

17. Invisible-Fragile Watermark and Its Applications
The invisible-fragile watermark is embedded in
such a way that any manipulation or modification
of the image would alter or destroy the watermark.
Applications:
Used for a trustworthy camera so the news agency can verify that an image is true to the original capture and has not been edited to falsify a scene.
Detect alteration of images stored in a digital library.

18. Desired Characteristics of Invisible Fragile Watermarks
Neither be noticeable to the viewer nor should
degrade the quality of the content.
Be readily modified when the image pixel values
have been altered.
Secure. This means that it is impossible to
recover the changes, or regenerate the
watermark after image alterations, even when
the watermarking procedure and/or the
watermark itself is known.
The amount of individual pixel modification
should be as small as possible

19. Dual Watermark and Its Applications
Dual watermark is a combination of a
visible and an invisible watermark.
In this type of watermark, an invisible watermark
is used as a backup for the visible watermark.

20. Dual Watermark

21. Watermarks attacks 1) Robustness Attacks
Robustness attacks attempt to diminish or remove the presence of watermarks in a suspect image without rendering the image useless
classified into two types: signal processing attacks, and analytic and algorithmic attack
Signal processing attack include common processing operations
such as compression, filtering, resizing, printing, and scanning.
Analytic and algorithmic attacks involve removal or weakening of watermarks in images based on the specific methods of watermark insertion and detection.
An example is the collusion attack where different watermarked versions of the same image are combined to generate a new image, reducing the strength of the watermark. ("Watermarking", 2017)
Referred also as cryptographic attack: Imbedding of new valid watermark rather then removing –Gives an attacker a chance to manipulated
The protected data as he wishes and then implant the new given key to replace the destroyed one thus making a corrupted image genuine
Sometimes deploy techniques such as brute force and oracle

22. ..Watermarks attacks 2) Presentation Attacks
the watermarked content is manipulated so a detector cannot find it
E.g misaligning a watermarked image can sometimes fool an automated detector such as a Webcrawler, even though the underlying pixel values are not changed.
Other examples of presentation attacks include rotation and enlargement.
In a presentation attack the watermark does not need to be removed or diminished. ("Watermarking", 2017)
Web Crawler sometimes known as Mosaic attack works by ;
1)Dividing the image into sub images with rendition instruction
2)Browser will be re-arranging the sub images to appear as the original
3)Sub images will be sufficiently small that no single image on its own will contain a recognizable mark

23. ..Watermarks attacks 3) Interpretation Attacks
Interpretation attacks seek to falsify invalid or multiple interpretations of a watermark.
For example, an attacker can attempt to make another watermark appear in the same watermarked image with strength equal to that of the owner’s watermark, creating an ownership deadlock.
The pixel values may or may not change.

24. ..Watermarks attacks 4) Legal Attacks
ability of an attacker to cast doubt on the watermarking scheme in the courts
This attacks rely on existing and future legislation on copyright laws and digital information ownership, the credibility of the owner and of the attacker, the financial strength of the owner versus that of the attacker, the expert witnesses, and the competence of the lawyers.
Counter measure: The use a robust watermarking scheme to eliminated doubts casted against legal evidences
As an aside, in a 2003 press release by Digimarc, a leading supplier of secure media solutions, it was reported that Corbis - a visual solutions provider (licensing images) - identified up to 50 cases of unauthorized uses of Corbis images per month using Digimarc digital watermarking solutions.

25. Conclusion Watermarking is an art of information hiding
There exit different types of digital Watermarks and attacks
Common applications of watermarking is to enable copyright ,image authentication and ownership protection

26. Class Activity
See “Know Your Currency” post under Discussion forum

27. Reference
Chen, K. (2005). Information Hiding, Digital Watermarking and Steganography. In Encyclopedia of Multimedia Technology and Networking (pp ). IGI Global. Know Your Currency (2017). Retrieved 19 September 2017, from Watermarking. (2017). Io.acad.athabascau.ca. Retrieved 19 September 2017, from
Rivest, Shamir, and Adelma :RSA encryption