By Elo Leung and Wing WongCS 265 Section 2

Spring 2004

Table of Contents1. Project Objectives2. Watermarking in General3. Attacks on Watermarks4. Desired Characteristics of Invisible Watermarks5. Spread Spectrum Watermarking

– Insert & Extract Watermark6. Example7. Advantages & Disadvantages8. Conclusion

Project Objectives

- Analyze the spread spectrum watermarking algorithm proposed by Cox et al.

- Demonstrate the application of Cox’s algorithm using a sample image file

Watermarking in Generalthe 3 components:

1. Watermark

2. Encoder – watermark insertion

3. Decoder and Comparator – watermark extraction and verification

Watermarking in Generalthe 3 components:1. Watermark2. Encoder3. Decoder and ComparatorEncoder

Original WatermarkedImage (I ) Image (I' )

Signature (S )

E

Figure provided by Mohanty [2].

Watermarking in GeneralUses 3 components:1. Watermark2. Encoder3. Decoder and Comparator

Decoder Comparator

Test Extracted match/Image (J ) Signature (S' ) mismatch

Origianal Image (I ) Origianal Signature (S )

D C

Figure provided by Mohanty [2].

Attacks on Watermark

Transmission

Lossy OtherCompression International

TamperingsProcessing

I

I'

Watermarked Object

Corrupted Object

Transmission

Typical Distortions and International Tampering

GeometricalDistortion

CommonSignal

Figure provided by Cox et al. [1].

Attacks on Watermark

Transmission

Lossy OtherCompression International

TamperingsProcessing

I

I'

Watermarked Object

Corrupted Object

Transmission

Typical Distortions and International Tampering

GeometricalDistortion

CommonSignal

Irreversible Data Loss

Quality Degradation

e.g. JPEG/MPEG

Attacks on Watermark

Transmission

Lossy OtherCompression International

TamperingsProcessing

I

I'

Watermarked Object

Corrupted Object

Transmission

Typical Distortions and International Tampering

GeometricalDistortion

CommonSignal

Specific for images/videos

rotation, translation, scaling, and cropping operations

Attacks on Watermark

Transmission

Lossy OtherCompression International

TamperingsProcessing

I

I'

Watermarked Object

Corrupted Object

Transmission

Typical Distortions and International Tampering

GeometricalDistortion

CommonSignal

analog-to-digital, digital-to-analogconversion, etc.

Attacks on Watermark

Transmission

Lossy OtherCompression International

TamperingsProcessing

I

I'

Watermarked Object

Corrupted Object

Transmission

Typical Distortions and International Tampering

GeometricalDistortion

CommonSignal

Rewatermarking

Desired Characteristics of Invisible Watermarks

1. Perceptually unnoticeable

2. Robust to common watermark attacks

3. Quality degradation upon removal of watermarks

4. Unambiguously identifies the owner of the digitized medium (audio, video, or image).

Spread Spectrum WatermarkingSpread Spectrum Watermark = Invisible Watermark

Key: • Insert watermark at perceptually significant regions

• Spread watermark throughout the data

**Data = audio, video, or image file

Spread Spectrum WatermarkingInsertion Process

Original Image (V)

Spectrum

Watermark (X) Insert Modified Normally Distributed watermark Spectrum

WatermarkedImage (V')

Determine percetually significant regions

Inverse FFT/DCT

FFT/DCT

Figure provided by Mohanty [2].

v'i = vi (1 + αxi)

Spread Spectrum WatermarkingExtraction Process

RecoveredImage (I')

RecoveredSpectrum

Original FFT/ Original Image (V) DCT Spectrum

ExtractedWatermark (X*)

does not similar? belong

to owner yes

belongs toowner

noOriginal Watermark (X)

-

Figure provided by Mohanty [2].

sim(X, X*) = (X X*) sqrt (X X*)

Example

(1) Original (2) Watermarked Differences of (1) & (2)

Advantages & DisadvantagesAdvantages:

• Not noticeable since the watermarks are spread out.

• Can’t be removed without severe quality degradation since watermarks are inserted at perceptually significant regions.

Disadvantages:

• Original watermark is required in the extraction process.

Conclusion

Spread spectrum watermarking:

• Can be used for audio, video, and image files

• Meets the desired characteristics of invisiblewatermarks – unnoticeable, robust, unambiguous

References:

[1]Ingemar J. Cox, et al., “Secure Spread Spectrum Watermarking for Multimedia”, IEEE Trans. on Image Processing, Vol. 6, No.12, Dec 1997, pp.1673-1687.  [2]   Saraju P. Mohanty, “Digital Watermarking: A Tutorial Review”, Department of Computer Science and Engineering, University of South Florida. [3]   Peter Meerwald, “Digital Image Watermarking in the Wavelet Transform Domain”, Master’s Thesis, Department of Scientific Computing, University of Salzburg, Austria, January 2001.

[4] http://www.cosy.sbg.ac.at/~pmeerw/Watermarking/source/

The End