DCT-based image-independent digital watermarking

Digital watermark is a technique to protect intellectual property in digital form by embedding an invisible signal (watermark) to original audio, image and video. In this paper, a frequency domain watermarking method for still image is proposed. It is based on discrete cosine transform. By making good use of the characteristics of the original image, a visually recognizable binary watermark is generated from the image and then embedded the watermark into the image. During watermarking, the techniques of image segmentation and pseudo-random permutation are used so as to be compatible with the JPEG compression standard and enhance the robustness. The method presented in this paper is image-independent and it is sensitive to luminance and contrast alteration. Experimental results show that the method is feasible and a threshold of normalized coefficient is given to judge whether the image is changed.