Digital watermarks have been proposed as a method for discouraging illicit copying and distribution of copyrighted material. This paper describes a method for the secure and robust copyright protection of digital images. The key contribution lies in the development of a fast iterative template matching algorithm based on log-log or log-polar maps. The algorithm exploits the properties of the Chirp-Z transform to obtain the accuracy needed in the detection of transformations in realistic watermarking applications. Test results verify the robustness of the method.