1. Image Watermarking
Chu, Hsi-Cheng

2. What is Image Watermarking?
A technique to to embed some secret information in the image +
image
watermarked image
watermark

3. What is Image Watermarking?
The embedded information can be extracted when needed
Detector
watermarked image
watermark

4. Watermarking Requirements
Imperceptibility
Robustness

5. Correlation-Based Watermarking Techniques
I(x,y)
Iw(x,y)
Multiply by
gain factor k
seed
Iw(x,y)=I(x,y)± k·W(x,y)
W(x,y): Pseudorandom Pattern {-1,1}

6. Watermark Detection RIw(x,y)W(x,y) > T → W(x,y) detected
< T → No W(x,y) detected
If detected, RIw(x,y)W(x,y) > 0 → bit ‘1’
or RIw(x,y)W(x,y) < 0 → bit ‘0’

7. Techniques for Transform Domains
DFT, DCT, DWT
More robust

8. Conclusions
The process of watermarking is a tradeoff among image quality, watermark capacity, robustness
Techniques for frequency domains are superior to techniques for the spatial domain