Robust watermarking using watermark spread canvass in DCT & DHT domain

Digital watermarking is a technique which allows an individual to add hidden copyright notices or other verification messages to digital audio, video, or image signals and documents. In this paper a novel robust image watermarking method based on Discrete Hartley Transform (DHT) and Discrete Cosine Transform (DCT) is presented. The watermarking image is spread on a canvass and is then embedded invisibly block by block either in DCT domain or in DHT domain in a block wise manner in the original image depending on the number of edges in each block of the original image. For this purpose, the threshold number of edges acts as a key. To extract the embedded image from the watermarked image, the same steps used in the embedding process are performed in reverse sequence. This technique is demonstrated to be robust against various attacks like Salt & Pepper, JPEG compression etc. even with severe degradation to the watermarked image.