Image watermark resistant to geometric attacks is the focus and difficulty point in the current research on watermarking. This paper proposes a Wavelet-domain watermarking algorithm against geometric attacks based on the SUSAN feature points matching. The algorithm embeds watermarks into each sub-band of the wavelet coefficients of the host image with different strength adaptively adjusted in terms of the gray level of them. The choice of the embedding strategy effectively guarantees good transparency and strong robustness of the watermark. Furthermore, the paper improves the SUSAN operator, to extract the feature points robust to geometric distortion from the watermarked image. Before watermark detection, it uses the transformation of the corresponding points to correct geometric distortion, which ensures successful extraction of the watermark. Experiment results show that the proposed algorithm has good transparency, and it is also robust to common image processing and geometric attacks.
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