It is a common practice in transform-do main fragile watermarking schemes for authentication purposes to watermark some selected transform coefficients so as to minimise embedding distortion. However, we point out in this work that leaving most of the coefficients unmarked results in a wide-open security gap for attacks to be mounted on them. A fragile watermarking scheme is proposed to implicitly watermark all the coefficients by registering the zero-valued coefficients with a key-generated binary sequence to create the watermark and involving the unwatermarkable coefficients during the embedding process of the embeddable ones. Non-deterministic dependence is established by involving some of the unwatermarkable coefficients selected according to the watermark from a 9-neighbourhood system in order to thwart different attacks such as cover-up, vector quantisation, and transplantation. No hashing and cryptography are needed in establishing the non-deterministic dependence.

Permanent distortion is one of the main drawbacks of all the irreversible watermarking schemes. Attempts to recover the original signal after the signal passing the authentication process are being made starting just a few years ago. Some common problems, such as salt-and-pepper artifacts due to intensity wraparound and low embedding capacity, can now be resolved. However, we point out in this work that there are still some significant problems remain unsolved. Firstly, the embedding capacity is signal-dependent, i.e., capacity varies significantly depending on the nature of the host signal. The direct impact of this ill factor is compromised security for signals with low capacity. Some signal may be even non-embeddable. Secondly, while seriously tackled in the irreversible watermarking schemes, the well-recognized problem of block-wise dependence, which opens a security gap for the vector quantization attack and transplantation are not addressed by the researchers of the reversible schemes. It is our intention in this work to propose a reversible watermarking scheme with near-constant signal-independent embedding capacity and immunity to the vector quantization attack and transplantation. 1 1.

Picture archiving and communication systems (PACS) are typical information systems, which may be undermined by unauthorized users who have illegal access to the systems. This paper proposes a role-based access control framework comprising two main components – a content-based steganographic module and a reversible watermarking module, to protect mammograms on PACSs. Within this framework, the content-based steganographic module is to hide patients ’ textual information into mammograms without changing the important details of the pictorial contents and to verify the authenticity and integrity of the mammograms. The reversible watermarking module, capable of masking the contents of mammograms, is for preventing unauthorized users from viewing the contents of the mammograms. The scheme is compatible with mammogram transmission and storage on PACSs. Our experiments have demonstrated that the content-based steganographic method and reversible watermarking technique can effectively protect mammograms at PACS.

Abstract—Information hiding for authenticating and verifying the content integrity of the multimedia has been exploited extensively in the last decade. We propose the idea of using genetic algorithm and non-deterministic dependence by involving the unwatermarkable coefficients for digital image authentication. Genetic algorithm is used to intelligently select coefficients for watermarking in a DCT based image authentication scheme, which implicitly watermark all the un-watermarkable coefficients also, in order to thwart different attacks. Experimental results show that such intelligent selection results in improvement of imperceptibility of the watermarked image, and implicit watermarking of all the coefficients improves security against attacks such as cover-up, vector quantization and transplantation. Keywords—Digital watermarking, fragile watermarking, genetic algorithm, Image authentication. I.