A Digital Watermark Technique Based on the Wavelet Transform and Its Robustness on Image Compression and Transformation∗

In this paper, we propose two methods of digital watermark for image signals based on the wavelet transform. We classify wavelet coefficients as insignificant or significant by using zerotree which is defined in the embedded zerotree wavelet (EZW) algorithm [13]. In the first method, information data are embedded as watermark in the location of insignificant coefficients. In the second method, information data can be embedded by thresholding and modifying significant coefficients at the coarser scales in perceptually important spectral components of image signals. Information data are detected by using the position of zerotree’s root and the threshold value after the wavelet decomposition of an image in which data hide. It is shown from the numerical experiments that the proposed methods can extract the watermark from images that have degraded through several common signal and geometric processing procedures. key words: digital watermark, copyright protection, wavelet transform, image signal