Geometrically Invariant Image Watermarking via Robust Perceptual Hashes

We consider the problem of blind watermark detection from an image, when the image has undergone a geometric attack. Existing schemes for solving this problem involve insertion of periodic marks or templates, invariant properties of transforms, and feature point based techniques. A major deficiency of these approaches is either a security leak (owing to redundancy in the mark) and/or poor watermark detection performance esp. under lossy geometric attacks, e.g. cropping. In this paper, we introduce a novel watermark synchronization paradigm by using perceptual image hashes. We exploit the fact that a perceptual hash acts as a robust as well as randomized digest of image content, and use it to embed a synchronization mark into the image. Unlike existing synchronization schemes, our synchronization mark has favorable security and robustness to adversarial attacks and hence, cannot be easily removed. Experimental results confirm that our proposed algorithm has significantly lower watermark detection error probabilities than existing methods.