Robustness of wavelet domain watermarking against scaling attack

Robustness of image watermarking algorithms is challenged by applying various attacks on the watermarked images. One of such attacks is scaling. In this paper, we first demonstrate that structure of the scaling attack resembles that of discrete wavelet transform (DWT). Consequently, we are able to show that particular class of DWT watermarking method is robust against the scaling attack. It is shown that regardless of watermarking method, embedding a watermark in the approximation coefficients of wavelet transform makes the watermark more robust against the scaling attacks. In this paper, not only we provide the necessary condition for the robustness of DWT watermarking, but also we provide the sufficient criterion for this robustness to hold, based on the scaling attack level versus the number of DWT levels.