Dual detection of watermarks embedded in the DCT domain

Spatial domain watermarking techniques do not fully consider the frequency characteristics of an image, so they are vulnerable to frequency domain attacks like JPEG compression. On the other hand, DCT domain watermarking techniques are subject to geometric attacks such as rotation and resizing. To overcome these problems we propose a dual watermark detection scheme, detecting watermarks both in spatial and in DCT domains. Our method embeds a watermark in the DCT domain. For the spatial domain detection, we use a synchronization technique based on block-based template matching to reverse the disordered alignment caused by two important geometric attacks, rotation and resizing. An equivalent pattern of the watermark is extracted in the spatial domain. The extracted watermark is then correlated for detection with the watermark obtained by taking inverse DCT to the original watermark, Results show that the proposed dual detection is robust to both geometric attacks and other signal processing attacks.