This paper introduces amplitude-only images to image trading systems in which not only the copyright of images but also the privacy of consumers are protected. In the latest framework for image trading systems, an image is divided into an unrecognizable piece and a recognizable but distorted piece to simultaneously protect the privacy of a consumer and the copyright of the image. The proposed scheme uses amplitude-only images which are completely unrecognizable as the former piece, whereas the conventional schemes leave recognizable parts to the piece which degrades privacy protection performance. Moreover, the proposed scheme improves the robustness against copyright violation regardless of the used digital fingerprinting technique, because an amplitude-only image is larger than the piece in the conventional scheme. In addition, phase-only image is used as the second piece in the proposed scheme, the consumer can confirm what he/she bought. Experimental results show the effectiveness of the proposed scheme.

In this paper, a compression-friendly copyright- and privacy-protected image trading system is proposed. In the image trading system, the copyright of the image and the consumer's privacy is important. In addition, it should preserve existing image compression standards. In the proposed method, for privacy protection, the content provider (CP) multiplies random signs to the discrete wavelet transformed (DWTed) coefficients of an image to generate the visually encrypted image. The proposed visually protected images can be efficiently compressed by using JPEG 2000 which compresses the image in the DWTed domain as well. For copyright protection, the trusted third party (TTP) applies digital fingerprinting to the image in the encrypted domain. While in the conventional system, the amplitude-only image (AOI) which is the inversely transformed amplitude spectra of an image is used for privacy protection. Since, the AOI consists of real numbers, to store and transmit the AOI, it has to be quantized before compression. Therefore, quantization errors cannot be avoided in the conventional system. On the other hand, the proposed method applies the digital fingerprint in the DWTed domain, so clipping errors in decoding the image by the TTP is avoided. In addition, only a seed number which is input to a pseudo random number generator is shared between the CP and the consumer, whereas an extra image is shared in the conventional systems. Experimental results show that the proposed system is efficient in terms of privacy protection, compression performance, quality of fingerprinted images, and correct fingerprint extracting performance.

This paper proposes a visual secret sharing (VSS) scheme with efficient pixel expansion which prevents malicious share holders from deceiving an honest share holder. A VSS scheme encrypts a secret image into pieces referred to as shares where each party keeps a share so that stacking a sufficient number of shares recovers the secret image. A cheat prevention VSS scheme gives another piece to each party for verifying whether the share presented by another party is genuine. The proposed scheme improves the contrast of the recovered image and cheat-prevention functionality by introducing randomness in producing pieces for verification. Experimental results show the effectiveness of the proposed scheme.

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 inversely transformed phase components, in comparison with the conventional systems.