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 Iw(x,y) I(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