Digital watermarking technique using block correlation of DCT coefficients

In recent years, high-quality digital media have spread rapidly. Accompanying the diffusion of digital media which can be simply copied and edited without deterioration of quality, research on digital watermarking techniques is being pursued as a means of preventing illegal copying and protecting copyright. In this paper, we will propose a technique for digital watermarking dealing with color images. The embedding of watermark information by the proposed technique is performed by using interblock correlation of the DCT coefficients of the brightness of a color image, and the strength of the watermark information to be embedded will vary with the visual features of the image. It is strongly embedded at places where there are intense changes of the brightness value and is weakly embedded at places where there are only mild changes of the brightness value. Since no distinction between the original image and the image in which the watermark information is embedded can be made visually, third-party estimation of the position where the embedding is performed is very difficult. Moreover, detection of the embedded watermark information can be performed without referring to the original image and the parameters used in embedding. It has been confirmed by experiments that the watermark information embedded by the proposed technique is robust to JPEG compression and Gaussian noise. © 2002 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 85(9): 23–31, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.10069