A Joint DWT-DCT Based Robust Digital Watermarking Algorithm for Ownership Verification of Digital Images

Abstract

In this paper, a robust digital image watermarking algorithm based on joint Discrete Wavelet Transform and Discrete Cosine Transform (DWT-DCT) is proposed. The proposed system provides imperceptibility and higher robustness against common signal processing attacks. A binary watermarked image is embedded in certain subbands of a 3-level DWT transformed coefficients of a host image. Then, DCT coefficients of each selected DWT subband is computed. A randomly generated two-dimensional key is used to encrypt the watermark. This 2D key provides security to the image and ownership copyrights. The PN-sequences of the encrypted watermark bits are embedded in the coefficients of the corresponding DCT middle frequencies providing higher security. In extraction stage, the same approach as that of the embedding process is used to extract the DCT middle frequencies of each subband. Finally, correlation between mid-band coefficients and PN-sequences is calculated to determine watermark bit which is again post-processed by the two-dimensional key generated to derive the actual watermark. Experimental results show that the proposed method based on joint procedure of DWT-DCT may be used for watermarking the digital images.