Feature Point Based Image Watermarking Scheme in Contourlet Domain Against Geometrical Attacks

Image watermarking resistant to geometrical attacks is the hotspot and challenging task in the state-of-the-art research on watermarking. Even an invisible affine transformation can invalidate most existing watermarking algorithms. This the authors analyse and discuss the characteristic of contourlet transform and Harris-Affine detector, and on this basis, propose a novel contourlet-domain watermarking algorithm against geometric attacks based on the affine-invariant feature points and characteristics of regions. First, the proposed scheme uses contourlet transform to extract multidirectional and multiscale texture information, and then obtains the feature points invariant to the affine transformation from the low and middle directional subbands by Harris-Affine detector. Second, the feature regions are adaptively computed by the feature scale of the local structure and normalized by U transform. The watermarking is emdedded adaptively in those characteristic regions which are normalized. Finally, by vector quantization, several copies of the watermark are embedded into the no overlapped local feature regions in different directional subbands. During detection, the resynchronization is achieved through feature points. And the embedded sequence can be extracted by “majority principles” without resorting to the original host image. Experimental results show that the proposed algorithm has good transparency and is very robust to common image processing and geometric attacks.