Robust multiple watermarks for medical image based on DWT and DFT

Medical images must be stored in a secure way to preserve unauthorized disclosure of patient data. This paper proposes an algorithm of robust multiple watermarks to serve these purposes using DWT and DFT. A part of sign sequence of DWT and DFT coefficients are used as feature vector for enhancing the robustness against rotation attacks, scaling attacks, translation attacks and cropping attacks. Moreover, the content of medical image remains unchanged with our proposed algorithm which is one kind of the zero-watermarking technology. We describe how to extract the feature vector of medical image, and then, embed and extract the multiple watermarks. The results of experiment indicate that the watermark scheme has strong robustness, and can embed much more data compared with the existing watermarking techniques.