Robust Watermarking Scheme Based on Discrete Wavelet Transform (DWT) and Discrete Cosine Transform (DCT) for Copyright Protection of Digital Images

In this paper robustness of image watermarking algorithm in transform domain using combined DWT-DCT is evaluated. Host image is decomposed up to 3-levels using discrete wavelet transform. DCT transform of selected DWT sub band coefficients blocks are computed. Binary Watermark is embedded in the DCT transform of each selected DWT sub-band. For embedding watermark bits corresponding random number sequence is added in the middle frequency coefficients of the DCT block. To extract the watermark same procedures as the embedding process is used. Correlation between mid-band coefficients and random-sequences is calculated to determine watermarked bits. The implementation of algorithm shows good imperceptibility and higher robustness against common signal processing attacks.