A Privacy-Secure Content Trading System for Small Content Providers Using Semi-Blind Digital Watermarking

A privacy-secure content trading system based on semi-blind fingerprinting which provides privacy-secure content trading as secure as blind fingerprinting at feasible processing cost with sufficient robustness is evaluated in this paper. This system assures both a content provider and a purchaser of a fair trading which is effective in a market where purchasers deal with a number of small or not so reliable content providers. We have implemented the system in which a useful tool should be provided for the market by amending inherent defects of conventional methods. In the basic models of conventional fingerprinting, the user's security is guaranteed only under the premise that a content provider was perfectly trustworthy. Such premise makes a system unpractical. In order to cope with the problem, various fingerprinting schemes have been proposed in which cryptography technique utilized in order to protect user's privacy. However, these are found to be unpractical due to the heavy computation cost and insufficient robustness of watermarking against manipulations. The semi-blind fingerprinting fulfills the need for both feasibility and robustness by altering encryption into the one with image decomposition that could blind an image to be unrecognizable. Image decomposition and a customized embedding algorithm are implemented to a web-based system, whose perceptual condition of decomposed images and robustness of watermark has been evaluated.