A Watermark-Like Authentication Scheme for the Images and Graphics Based on Discrete Cosine Transform Domain

This paper proposed a watermark-like authentication scheme for the images and graphics based on discrete cosine transform (DCT) domain. This scheme does not modify the original data but just determines a mapping rule to go from the DCT coefficients of the authenticating logo to the DCT coefficients of the original image by torus automorphism. In the whole authenticating process, no original information is destroyed. Therefore, this scheme can be used in multimedia and authentication system that require high quality images. The result of experiment shows that this scheme has the following advantages compared to the current watermark-like scheme based on spatial domain: This scheme can save 30% space in storing the mapping rule. When the PSNR of the original image is above 30 dB, the PSNR of the authenticating logo extracted by this scheme is 4 dB higher. The authenticating process of this scheme does not include IDCT and DCT operations for JPEG form at images. The authenticating speed is improved so much.