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Controversial 'pixel' prior rule for JPEG adaptive steganography

Currently, the most successful model for image adaptive steganography is the framework of minimal distortion, in which a reasonable definition of costs can improve the security level. In the authors' previous work, they developed a rule for cost reassignment in spatial domain called the `controversial pixel prior (CPP)' rule, which defines controversial pixels by utilizing the controversies among several comparable schemes. The CPP rule gives controversial pixels higher modification priorities. In this study, they investigate migrating the CPP rule from the spatial domain to the joint photographic experts group (JPEG) domain and name it the J-CPP rule. In JPEG images, the cover elements are discrete cosine transform (DCT) coefficients and variant factors mayinfluence the distortion definition includingquantisation step, inter-blocks correlation and block energy. However, there is no evidence to reveal which factor is of highest priority for promoting security. In this work, they investigate which factor is more helpful in promoting J-CPP rule, and they finally determine to set the spatial block residual as a penalty to perfect J-CPP rule. Through extensive experiments on different JPEG steganographic algorithms and steganalysis features, they demonstrate that the J-CPP rule can improve the security of JPEG adaptive steganography.