Image watermarking-a spread spectrum application

This paper discusses the feasibility of coding a robust, undetectable, digital watermark on a standard 512*512 intensity image with an 24 bit RGB format. The watermark is capable of carrying such information as authentication or authorisation codes, or a legend essential for image interpretation. This capability is envisaged to find application in image tagging, copyright enforcement, counterfeit protection, and controlled access. The method chosen is based on linear addition of the watermark to the image data. The patterns adopted to carry the watermark are adaptations of m-sequences in one and two dimensions. The recovery process is based on correlation, just as in standard spread spectrum receivers. The technique is quite successful for one dimensional encoding with binary patterns, as shown for a variety of gray scale test images. A discussion of extensions of the method to two dimensions, RGB format and non-binary alphabets is presented. A critical review of other watermarking techniques is included