Abstract
The digital watermark technology is now drawing the attention as a new method of protecting copyrights for digital contents such as audio, image and video. It is realized by embedding information data about the copyright owner with an imperceptible form for human audio/visual systems. We present in this paper a method of digital watermark for image signals based on the discrete wavelet transform (DWT). In this method, information data can be embedded in the lowest frequency components of image signals by using a controlled quantization process. The data are then extracted by using both the quantization step-size and the mean amplitude of the lowest frequency components without access to the original image. Numerical experiments show that the proposed method provides a high-quality watermarked image and is robust against common signal processings such as JPEG compression, wavelet coding, additive noise, smoothing, reduction of grayscale level and scaling.