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D ig ital W ater mark ing Parag Agarwal {pxa016500@utdallas.edu} Agenda Background Terminology Applications Techniques Research topics References Information Hiding Information Hiding…..started with Steganography (art of hidden writing):

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d ig ital w ater mark ing

Digital Watermarking

Parag Agarwal

{pxa016500@utdallas.edu}

agenda
Agenda
  • Background
  • Terminology
  • Applications
  • Techniques
  • Research topics
  • References
information hiding
Information Hiding
  • Information Hiding…..started with

Steganography (art of hidden writing):

The art and science of writing hidden messages in such a way that no one apart from the intended recipient knows of the existence of the message. The existence of information is secret.

Stego – Hidden , Graphy – Writing  ‘art of hidden writing’

steganography dates back to 440 bc
Steganography(dates back to 440 BC)
  • Histaeus used his slaves (information tattooed on a slave’s shaved head )

Initial Applications of information hiding  Passing Secret messages

microchip application
Microchip - Application
  • Germans used Microchips in World War II

Initial Applications of information hiding  Passing Secret messages

what is a watermark
What is a watermark ?

What is a watermark ?A distinguishing mark impressed on paper during manufacture; visible when paper is held up to the light (e.g. $ Bill)

Application for print media  authenticity of print media

what is a watermark7
What is a watermark ?

Digital Watermarking: Application of Information hiding (Hiding Watermarks in digital Media, such as images)

Digital Watermarking can be ?

- Perceptible (e.g. author information in .doc)

- Imperceptible (e.g. author information in images)

Visibility is application dependent

Invisible watermarks are preferred ?

applications
Applications

Copyright Protecton:To prove the ownership

of digital media

Eg. Cut paste of images

Hidden Watermarks represent the copyright information

applications9
Applications

Tamper proofing: To find out if data was tampered.

Eg. Change meaning of images

Hidden Watermarks track change in meaning

Issues: Accuracy of detection

applications10
Applications

Quality Assessment: Degradation of Visual Quality

Loss of Visual Quality

Hidden Watermarks track change in visual quality

comparison
Comparison
  • Watermarking Vs Cryptography

Watermark D  Hide information in D

Encrypt D  Change form of D

watermarking process
Watermarking Process
  • Data (D), Watermark (W), Stego Key (K), Watermarked Data (Dw)

Embed (D, W, K) = Dw

Extract (Dw) = W’ and compare with W

(e.g. find the linear correlation and compare it to a threshold)

Q.How do we make this system secure ?

A. K is secret (Use cryptography to make information hidden more secure)

watermarking process example embedding dw d w
Watermarking ProcessExample – Embedding (Dw = D + W)
  • Matrix representation (12 blocks – 3 x 4 matrix)

(Algorithm Used: Random number generator RNG), Seed for RNG = K, D = Matrix representation, W = Author’s name

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watermarking process example extraction
Watermarking ProcessExample – Extraction
  • The Watermark can be identified by generating the random numbers using the seed K

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data domain categorization
Data Domain Categorization
  • Spatial Watermarking

Direct usage of data to embed and extract Watermark

e.g. voltage values for audio data

  • Transform Based Watermarking

Conversion of data to another format to embed and extract.

e.g. Conversion to polar co-ordinate systems of 3D models, makes it robust against scaling

extraction categorization
Extraction Categorization
  • Informed (Private)

Extract using {D, K, W}

  • Semi - Blind (Semi-Private)

Extract using {K, W}

  • Blind (Public)

Extract using {K}

- Blind (requires less information storage)

- Informed techniques are more robust to tampering

robustness categorization
Robustness Categorization
  • Fragile (for tamper proofing e.g. losing watermark implies tampering)
  • Semi-Fragile (robust against user level operations, e.g. image compression)
  • Robust (against adversary based attack, e.g. noise addition to images)

This categorization is application dependent

categorization of watermark
Categorization of Watermark

Eg1. Robust Private Spatial Watermarks

Eg2. Blind Fragile DCT based Watermarks

Eg3. Blind Semi-fragile Spatial Watermarks

watermarking example
Watermarking Example

Application: Copyright Protection

Design Requirements:

- Imperceptibility

- Capacity

- Robustness

- Security

imperceptibility
Imperceptibility

Watermarking

Stanford Bunny 3D Model

Visible Watermarks in Bunny Model  Distortion

Watermarking

Invisible Watermarks in Bunny Model  Minimal Distortion

Stanford Bunny 3D Model

robustness
Robustness

Adversaries can attack the data set and

remove the watermark.

Attacks are generally data dependent

e.g. Compression that adds noise can be used as an attack to remove the watermark. Different data types can have different compression schemes.

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Robustness
  • Value Change Attacks

- Noise addition e.g. lossy compression

- Uniform Affine Transformation e.g. 3D

model being rotated in 3D space OR

image being scaled

If encoding of watermarks are data value dependent 

Watermark is lost  Extraction process fails

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Robustness
  • Sample loss Attacks

- Cropping e.g. Cropping in images

- Smoothing e.g. smoothing of audio

signals e.g. Change in Sample rates

in audio data change in sampling rat

results in loss of samples

If watermarks are encoded in parts of data set which are

lost  Watermark is lost  Extraction process fails

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Robustness
  • Reorder Attack

- Reversal of sequence of data values e.g. reverse filter in audio signal reverses the order of data values in time

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Attack

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Samples in time

Samples in time

If encoding is dependent on an order and the order is changed  Watermark is lost Extraction process fails

capacity
Capacity
  • Multiple Watermarks can be supported.
  • More capacity implies more robustness since watermarks can be replicated.

Spatial Methods are have higher capacity than transform techniques ?

security
Security
  • In case the key used during watermark is lost anyone can read the watermark and remove it.
  • In case the watermark is public, it can be encoded and copyright information is lost.
watermarking algorithm design requirements
Watermarking Algorithm Design Requirements
  • As much information (watermarks) as possible

 Capacity

  • Only be accessible by authorized parties

 Security

  • Resistance against hostile/user dependent changes

 Robustness

  • Invisibility

 Imperceptibility

tamper proofing
Tamper proofing
  • Robustness against user related operations – compression, format conversion
  • Accuracy of Detection – Only changes in meaning should be detected
references
References
  • http://en.wikipedia.org/wiki/Steganography
  • http://en.wikipedia.org/wiki/Digital_watermark
  • http://www.cypak.com/pictures/med/Cypak%20microchip.jpg

THANK YOU !