This letter proposes an efficient compression scheme for the copyright-and privacy-protected image trading system. The proposed scheme multiplies pseudo random signs to amplitude components of discrete cosine transformed coefficients before the inverse transformation is applied. The proposed scheme efficiently compresses amplitude-only image which is the inversely transformed amplitude components, and the scheme simultaneously improves the compression efficiency of phase-only image which is the

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... inversely transformed phase components, in comparison with the conventional systems. key words: digital fingerprinting, trusted third party, random phase flipping, quantization, JPEG 2000