Affine-Invariant Image Watermarking Using the Hyperbolic Chirp

Image watermarking is the robust, imperceptible embedding of a small quantity of data into a digital image, and the subsequent recovery of this data, perhaps after the watermarked image has been distorted. We present a new watermarking technique which is robust to many image distortions, in particular arbitrary affine transformations of the image. The method achieves its robustness through the use of one-dimensional chirp functions. An affine-invariant detection method exists for such functions using a Radon transform, yet they are not detected trivially by a malicious attacker. The method also provides a way to determine any affine transformation applied to the watermarked image by using an affine-invariant property of groups of intersecting lines.