Image Watermarking

Image WatermarkingImage Watermarking

Chu, Hsi-Cheng

What is Image Watermarking?What is Image Watermarking?

A technique to to embed some secret information in the image

+image

watermark

watermarked image

What is Image Watermarking?What is Image Watermarking?

The embedded information can be extracted when needed

watermarked image Detector watermark

Watermarking RequirementsWatermarking Requirements

Imperceptibility

Robustness

Correlation-Based Correlation-Based Watermarking TechniquesWatermarking Techniques

Multiply by gain factor k

±

seed

I(x,y)

Iw(x,y)

W(x,y): Pseudorandom Pattern {-1,1}

Iw(x,y)=I(x,y)± k·W(x,y)

Watermark DetectionWatermark 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’

x y

wyxWyxI yxWyxIN

Rw

),(),(1

),(),(

x yx y

yxWyxWN

yxWyxIN

),(),(1

),(),(1

Techniques for Techniques for Transform DomainsTransform Domains

DFT, DCT, DWT

More robust

ConclusionsConclusions

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