Secure
Spread Spectrum
Watermarking for Multimedia
Ishani Vyas
CS590 Winter 2008
Agenda
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To explain about watermarking characteristics
How to insert watermark in spread spectrum
Structure of the Watermark
Experimental Result
Characteristics of Watermarking
Unobtrusive
Perceptually invisible or presence should not interfere with work being
protected
 Robust
Difficult to remove. May be removed sufficient knowledge of the process of
insertion. Available of Partial Knowledge-Result in degradation in data
fidelity.
Watermark should be robust to
Common Signal Processing-should be retrievable even if its operations
are applied to the data. For example D/A&A/D conversion,resampling
,requantization.
 Common geometric distortions (image and video data)- Watermarks in
image and video data should be immune from geometric image operations
such as rotation, translation, cropping and scaling
Collusion and Forgery- Watermark should be robust to collusion by multiple
individuals who each posses a watermarked copy of data.
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Cont
Watermark should be robust to combining copies of
same data set to destroy the watermarks
 Universal – apply same digital watermark algorithm to all
three media under consideration.
 Unambiguous- Retrieval of the watermark should
unambiguously identify the owner.
Why need of Spread Spectrum
watermarking
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The previous methods have not explicitly identified the perceptually
most significant components of a signal as the destination for the
watermark.
Key insight of this paper is that the watermark must be placed in
perceptually significant regions of the data despite the risk of
potential fidelity distortions.
Apply watermarking in significant spectral components of a signal.
How common signal transformations, (i.e compression, quantization
and manipulation) affects the frequency spectrum of a signal.
Watermark should be embedded in the data`s perceptually
significant frequency components.
But how to insert watermark into significant components of
frequency spectrum without any distortions.
Watermarking in frequency
domain
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Lossy compression is an operation that usually eliminates
perceptually non-salient components of an image or sound.
To preserve watermark in the face of such an operation, watermark
must be placed in the perceptually significant regions of the
data.Data loss usually occurs among the high frequency
components .
Geometrics distortions specific to image and video.(Rotation,scaling
,translation,cropping)- minimum 4-9 points between the original and
the distorted watermark image..Again loss of data at high frequency
spectral regions of the image.
Common signal distortion(D/A&A/D, resampling ,requantization,
including dithering and recompression and common signal
enhancements to image contrast/or color)
Spread Spectrum coding of
watermark
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How to insert the watermark into most significant region
of an spectrum without such alteration become noticable.
Structure of Watermark
Experimental Result
Watermarked image
Experiment 1:Uniqueness of
Watermark
Experiment 2:Image Scaling
Experiment3: JPEG coding
distortion
Experiment 4:Dithering
Distortion
Experiment 5:Clipping
Experiment 6:Print ,Xerox or
scan
Experiment 7:Attack by
watermarking watermarked image
Experiment 8:Attack by
collusion