Compared to the prominent role digital images play in nowadays multimedia society, research in the field of image authenticity is still in its infancy. Only recently, research on digital image forensics has gained attention by addressing tamper detection and image source identification. However, most publications in this emerging field still lack rigorous discussions of robustness against strategic counterfeiters, who anticipate the existence of forensic techniques. As a result, the question of trustworthiness of digital image forensics arises. This work will take a closer look at two state-of-theart forensic methods and proposes two counter-techniques; one to perform resampling operations undetectably and another one to forge traces of image origin. Implications for future image forensic systems will be discussed.

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--ZusammenfassnngSpacetime Representations of Computational Structures. A general theory for characterizing and then realizing algorithms in hardware is given. The physical process of computation is interpreted in terms of a graph in physical space and time, and then an embedding into this graph of another graph which characterizes data flow in particular algorithms is given. The types of the special class of computational structures called systolic arrays which can occur physically are completely described, and a technique is developed for mapping the graph of a particular systolic algorithm into a physical array. Examples illustrate the methodology. AMS

Abstract. This paper deals with strategies to dramatically reduce the complexity for embedding based on syndrome coding. In contrast to existing approaches, our goal is to keep the embedding efficiency constant, i.e., to embed less complexly without increasing the average number of embedding changes, compared to the classic Matrix Embedding scenario.Generally, our considerations are based on structured codes, especially on BCH Codes. However, they are not limited to this class of codes.We propose different approaches to reduce embedding complexity concentrating on both syndrome coding based on a parity check matrix and syndrome coding based on the generator polynomial.