A digital watermark for images using the wavelet transform

The digital watermark technology is now drawing the attention as a new meth od of protecting copyrights for digital contents such as audio, image and v ideo. It is realized by embedding information data about the copyright owne r 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 dis crete wavelet transform (DWT). In this method, information data can be embe dded in the lowest frequency components of image signals by using a control led quantization process. The data are then extracted by using both the qua ntization step-size and the mean amplitude of the lowest frequency componen ts without access to the original image. Numerical experiments show that th e proposed method provides a high-quality watermarked image and is robust a gainst common signal processings such as JPEG compression, wavelet coding, additive noise, smoothing, reduction of grayscale level and scaling.