Digital Image Watermarking Technique Using Discrete Wavelet Transform and Discrete Cosine Transform

Digital watermarking has been proposed as a viable solution to the need of copyright protection and authentication of multimedia data in a networked environment, since it makes possible to identify the author, owner, distributor or authorized consumer of a document. In this paper a new watermarking technique to add a code to digital images is presented: the method operates in the frequency domain embedding a pseudo-random sequence of real numbers in a selected set of DCT coefficient and a new method for digital image watermarking which does not require the original image for watermark detection. The watermark is added in selected coefficients with significant image energy in the transform domain in order to ensure non-erasability of the watermark. Advantages of the proposed method include: improved resistance to attacks on the watermark, implicit visual masking utilizing the time-frequency localization property of wavelet transform and a robust definition for the threshold which validates the watermark. . Experimental results demonstrate that this proposed technique is robust to most of the signal processing techniques and geometric distortions.