By Elo Leung and Wing Wong CS 265 Section 2 Spring 2004

Table of Contents 1.Project Objectives 2.Watermarking in General 3.Attacks on Watermarks 4.Desired Characteristics of Invisible Watermarks 5.Spread Spectrum Watermarking – Insert & Extract Watermark 6.Example 7.Advantages & Disadvantages 8. 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 General the 3 components: 1.Watermark 2.Encoder – watermark insertion 3.Decoder and Comparator – watermark extraction and verification

Watermarking in General the 3 components: 1.Watermark 2.Encoder 3.Decoder and Comparator Figure provided by Mohanty [2].

Watermarking in General Uses 3 components: 1.Watermark 2.Encoder 3.Decoder and Comparator Figure provided by Mohanty [2].

Attacks on Watermark Figure provided by Cox et al. [1].

Attacks on Watermark Irreversible Data Loss Quality Degradation e.g. JPEG/MPEG

Attacks on Watermark Specific for images/videos rotation, translation, scaling, and cropping operations

Attacks on Watermark analog-to-digital, digital-to-analog conversion, etc.

Attacks on Watermark 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 Watermarking Spread Spectrum Watermark = Invisible Watermark Key: Insert watermark at perceptually significant regions Spread watermark throughout the data **Data = audio, video, or image file

Spread Spectrum Watermarking Insertion Process Figure provided by Mohanty [2]. v' i = v i (1 + αx i )

Spread Spectrum Watermarking Extraction Process Figure provided by Mohanty [2]. sim(X, X*) = (X X*) sqrt (X X*)

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

Advantages & Disadvantages Advantages: 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 invisible watermarks – 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 [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 [4]

The End