1. Digital Watermarking (cont.)
Multimedia Security
Digital Watermarking (cont.)
Lecture 3

2. Spread Spectrum Method
• Spread spectrum coding of a watermark
- frequency domain of the image => communication channel
- watermark => the signal transmitted through the channel
the watermark W = w,,...,wn
each wi is chosen according to zero-mean Gaussian Distribution the image X is transform by full-frame DCT
n highest magnitude coefficients (except DC) are chosen: y1,...,yn
Embedding: y' i = yi + a wi Extracting: wi = (yi* - yi) / a
similarity = correlation (W,W *)

3. Spread Spectrum Method (cont.)

4. Spread Spectrum Method (cont.)
• Watermark detector
Watermark detector response to 1000 randomly generated watermarks 15

5. Perceptually Masking Method

6. Perceptually Masking Method (cont.)
• Frame from “pingpong”
Similarity value
• The watermark 17

7. Digimarc Watermarking
• A commercial watermarking software -
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8. Watermarking for Audio
• Phase Coding
- Inserting the watermark by modifying the phase of each frequency component
• Spread Spectrum Method
- The watermark code is spread over the available frequency band, and then attenuated and added as additive random noise
• Perceptual Method
- The watermark is generated by filtering a PN-sequence with a filter that approximates the frequency masking characteristics of HAS
- Weighting the watermark in the time domain to account for temporal masking 19

9. Watermarking for Audio (cont.)
• Watermark generator 20

10. Watermarking for Audio (cont.)
• Watermark detection 21

11. Watermarking for Polygonal Models
• 3D models watermarking
- vertex coordinates
- vertex topology (connectivity)
Embedded pattern Simplified polygonal 22

12. Limitations of Watermarking
Basic watermarking steps 23

13. Limitations of Watermarking (cont.)
• Counterfeit 24

14. Digital watermark