DCT-based image-independent digital watermarking

Digital watermarking is a technique to protect intellectual property in digital form by embedding an invisible signal (watermark) into the original audio, image and video. In this paper, a frequency domain watermarking method for a still image is proposed. It is based on the 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 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 the normalized coefficient is given to judge whether the image is changed