Digital Water Marking PPt

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Digital Water Marking PPt Powered By Docstoc
					 Digital Watermarking



Presentation By
               Aswini P
Agenda
 Background
 Terminology

 Applications

 Techniques
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.
                     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
   Germans used Microchips in World War II




Initial Applications of information hiding  Passing Secret messages
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 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 ?
What Can Be Watermarked?
   Multimedia data.
     Video.
     Audio.
     Still Images.
     Documents.

 Software.
 Hardware designs.
Multimedia Watermarks
 A digital watermark is a “secret key dependent”
  signal “inserted” into digital multimedia data.
 Watermark can be later detected/extracted in
  order to make an assertion about the data.
 A digital watermark can be.
     Visible (perceptible).
     Invisible (imperceptible).
Applications
Copyright Protection: To prove the ownership
of digital media




 Eg. Cut paste of images




Hidden Watermarks represent
the copyright information
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
Applications
Quality Assessment: Degradation of Visual Quality




                      Loss of Visual Quality


          Hidden Watermarks track change in visual quality
Comparison
   Watermarking Vs Cryptography

    Watermark D  Hide information in D

    Encrypt D  Change form of D
Requirements
   Requirements vary with application. For
    example:
       Perceptually transparent - must not perceptually
        degrade original content.
       Robust - survive accidental or malicious attempts at
        removal.
       Oblivious or Non-oblivious - Recoverable with or
        without access to original.
       Capacity – Number of watermark bits embedded.
       Efficient encoding and/or decoding.
Contradicting Requirements


       Perceptual Transparency



     Payload             Robustness   Security




      Oblivious vs. Non-Oblivious
Watermarking Example
Application: Copyright Protection
Design Requirements:
- Imperceptibility
- Capacity
- Robustness
- Security
Imperceptibility


                       Watermarking

     Stanford Bunny 3D Model           Visible Watermarks in
                                       Bunny Model  Distortion




                        Watermarking


     Stanford Bunny 3D Model           Invisible Watermarks in Bunny
                                       Model  Minimal Distortion
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.
  Robust Watermarking Techniques - A
  Communications Framework



          Media Carrier                          Media Carrier



         Coding and                              Decoding and
Water-
                             X        +
         Modulation                              Demodulation    Watermark
mark


             HVS
                          Noise/Attack Channel
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
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
Robustness
   Reorder Attack
     - Reversal of sequence of data values e.g. reverse filter
        in audio signal reverses the order of data values in
        time



    0        1             1            1      1        0
                               Attack
    1        2             3            3       2         1

         Samples in time                     Samples in time


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


               I(x,y)          IW (x,y)




                  Multiply by gain
   k                  factor k             IW(x,y)= I(x,y)+ k  W(x,y)

                                           RI 'W ( x , y )W ( x , y )  T 
                                                          W(x,y) detected
                                                              T 
       W (x,y): Pseud o Rand om Pattern {-1,0,1}
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
   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.
Watermark Attacks
   Active Attacks.
     Hacker attempts to remove or destroy the
      watermark.
     Watermark detector unable to detect watermark.
     Key issue in proof of ownership, fingerprinting, copy
      control.
     Not serious for authentication or convert
      communication.
Watermark Attacks
   Passive Attacks.
     Hacker tries to find if a watermark is present.
     Removal of watermark is not an aim.
     Serious for covert communications.

   Collusion Attacks.
     Hacker uses several copies of watermarked data
      (images, video etc.) to construct a copy with no
      watermark.
     Uses several copies to find the watermark.
     Serious for fingerprinting applications.
Watermark Attacks
   Forgery Attacks.
     Hacker tries to embed a valid watermark.
     Serious in authentication.
     If hacker embeds a valid authentication watermark,
      watermark detector can accept bogus or modified
      media.
Example: Forging Photo I.D.

               Millionaire with
                   Swiss bank
                                    Bad
                     account
                                    Forgery!




                                   Thanks
                                  Hong Man,
                                     for this
                                    picture!




                 Assistant
                  Professor
Conclusion
   Legitimate businesses and webmasters have
    nothing to fear from copyright law or the new
    wave of on-line enforcement technology found in
    digital watermarks and tracking services. By
    using audio files and images only when they have
    obtained permission of the copyright owner or the
    appropriate licensing agency, webmasters should
    be free to continue making their sites audio
    visually appealing.
Questions
  ???

				
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Description: Digital Water Marking PPt