A DCT-Based Image Watermarking Algorithm Robust To Cropping and Compression.

Digital watermarking is a highly evolving field, which involves the embedding of a certain kind of information under a digital object (image, video, audio) for the purpose of copyright protection. Both the image and the watermark are most frequently translated into a transform domain where the embedding takes place. The selection of both the transform domain and the particular algorithm that is used for the embedding of the watermark, depend heavily on the application. One of the most widely used transform domains for watermarking of still digital images is the Discrete Cosine Transform domain. The reason is that the Discrete Cosine Transform is a part of the JPEG standard, which in turn is widely used for storage of digital images. In our research we propose a unique method for DCT-based image watermarking. In an effort to achieve robustness to cropping and JPEG compression we have developed an algorithm for rating the 8×8 blocks of the image DCT coefficients taking into account their embedding capacity and their spatial location within the image. Our experiments show that the proposed scheme offers adequate transparency, and works exceptionally well against cropping while at the same time maintains sufficient robustness to JPEG compression.