A class of authentication digital watermarks for secure multimedia communication

A new approach to digital signatures for imaging, which adapts well to mult imedia communications in lossy channels is introduced. Rather than attachin g the signature's bit-string as a file-header, it is invisibly etched into the image using a new watermarking algorithm. The watermark is "nonfragile, " tolerating small distortions but not malicious tampering aimed at modifyi ng the image's content. In particular, the rank-order relationship in local areas throughout the lowest level of the DWT is exploited to encode the wa termark. An edge-based message digest is used. The signature is in the form of binary data and the wavelet decomposition coefficients are modified acc ording to this binary sequence. The signature is also embedded and tested w ithin the SPIHT compression algorithm. The information capacity is studied and the experimental results confirm a logarithm relation between the bit r ate and the quantization level, which is similar to the Shannon's capacity theorem. Experiments are performed to examine the signature's transparencey and robustness.