A novel public digital watermarking for still images based on encryption algorithm

Digital watermarking has been proposed to solve the ownership problem and prevent various malicious attacks in the recent years. However, most proposed watermarking algorithms are kept secret. If the watermarking algorithm can be open, it is more convincing for authentication when there is an argument. In this paper, a novel robust digital watermarking scheme for still images with public watermarking algorithm is proposed. We find the significant frequency coefficients to locate the position for embedding the watermark. The watermark is a binary image logo that can represent its ownership. Its bitmap is reordered by random permutation. Then we employ a data encryption algorithm such as DES (data encryption standard) to encrypt the bitmap permutation index of the logo. Each image is processed to generate a unique ID. The original image and ID is promulgated in the Internet Web site or trust third party as DVCS. An error correction coding scheme is also used to protect the watermark. Simulation shows that our watermarked images are robust against various attacks. Our watermarking algorithm can be open to the public, but only the owner, who uses the encryption algorithm to encrypt the random permutation order of the logo bitmap with the secret key, can retrieve the embedded watermark exactly in the cover image and recover the logo. If there is an argument between the owner and the attacker the secret key and ID can be provided to the arbitrator to resolve the copyright issue more convincingly.