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Wavelet based digital image watermarking




A wavelet-based watermark casting scheme and a blind wa- termark retrieval technique are investigated in this research. An adap- tive watermark casting method is developed to rst determine signif- icant wavelet subbands and then select a couple of signi cant wavelet coecients in these subbands to embed watermarks. A blind watermark retrieval technique that can detect the embedded watermark without the help from the original image is proposed. Experimental results show that the embedded watermark is robust against various signal process- ing and compression attacks.

With the rapid growth of Internet technologies and wide availability of multimedia computing facilities, the enforcement of multimedia copyright protection becomes an important issue. Digital watermarking is viewed as an e ective way to deter content users from illegal distributing. In recent years, digital watermarking has been intensively studied to achieve this goal. We can classify digital watermarking into two classes depending on the do- main of watermark insertion, i.e. the spatial- and the frequency-domain watermarking. Spatial domain watermarking is easy to implement and requires no original image for watermark detection. However, it often fails under signal processing attacks such as l- tering and compression. Besides, the delity of the original image data can be severely degraded since the watermark is directly applied on the pixel values. Frequency domain watermarking generally provides more protection under most of the signal processing attacks. But the existing frequency-domain watermark algrithms require the original image for comparison in the watermark retrieval process, which is not practical for a huge image database. Furthermore, the necessity of progressive transmission is one of the requirements for Internet distribution. The lack of progressive transmission property in existing spatial- and frequency-domain watermarking algorithms limits their Internet

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