Contourlet-domain watermarking algorithm against geometric attacks based on feature template

Image watermarking resistant to geometric attacks is the hotspot and challenging point in the state-of-the-art research on watermarking. Even an invisible affine transformation can invalidate most existing watermarking algorithms. This paper analyses and discusses the characteristics of Contourlet transform, and on the basis above, proposes a novel Contourlet-domain watermarking algorithm against geometric attacks based on the feature template matching. The proposed algorithm includes four important techniques: (1) Puting coefficients into one group with the same coordinate in each finest directional subband. Then select the coefficient with the richest texture from each group as the coefficient to be embedded watermarking. Therefore, watermarking can be embedded into significant region as well as highly textured region of the host image; (2) For each coefficient of the selected subband, embeding watermarking with different strength adaptively adjusted in terms of the energy of its parent coefficient in the lowest subband, and the texture of its neighborhood coefficients in finer scale. The choice of embedding position and the embedding strategy above effectively guarantee good transparency and maximum robustness of the proposed algorithm; (3) Improving the Harris-Laplace operator, extract the feature points robust to geometric deformation as template from the embedded image using improved Harris-Laplace operator; (4) When detection, using the transformation between corresponding points in feature template to realize resynchronization, and determining existence of watermarking by statistical correlation between host image and watermarking. Experimental results show the proposed algorithm has good transparency and is very robust to common image processing and geometric attacks.