Copyright protection for digital image based on joint DWT-DCT transformation

Copyright protection of digital images has drawn much attention owing to fast development of the internet in recent years. In this paper a new robust digital image watermarking algorithm based on joint DWT-DCT transformation is proposed. This algorithm combines the visual characteristics of low frequency sub-image of DWT and the ability of DCT to remove correlation between DWT coefficients. Hence a real-time blind watermark algorithm whose coefficients are obtained through experiments is also proposed. To make the watermark more robust, we embed the watermark into the low-frequency coefficients of DCT. Experimental results show that the proposed algorithm is effective and robust for noise jamming, filtering, cutting and JPEG compression.