(Watermarked images stored in databases and transmitted over the Internet are usually compressed, sometimes to very high compression ratios. Therefore, the first challenge faced by digital watermarking algorithms is compression. JPEG and EZW (EmbeddedZero-TreeWavelet) compression are the two most common compression methods. JPEG is a compression method based on discrete cosine transform domain, while EZW is a compression method based on wavelet transform domain.)
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