A. De Rosa

A new decoder for the optimum recovery of nonadditive watermarks

Watermark detection, i.e., the detection of an invisible signal hidden within an image for copyright protection or data authentication, has classically been tackled by means of correlation-based techniques. Nevertheless, when watermark embedding does not obey an additive rule, or when the features the watermark is superimposed on do not follow a Gaussian pdf, correlation-based decoding is not the optimum choice. A new decoding algorithm is presented here which is optimum for nonadditive watermarks embedded in the magnitude of a set of full-frame DFT coefficients of the host image. By relying on statistical decision theory, the structure of the optimum is derived according to the Neyman-Pearson criterion, thus permitting to minimize the missed detection probability subject to a given false detection rate. The validity of the optimum decoder has been tested thoroughly to assess the improvement it permits to achieve from a robustness perspective. The results we obtained confirm the superiority of the novel algorithm with respect to classical correlation-based decoding.

Optimum decoding and detection of multiplicative watermarks

This work addresses the problem of optimum decoding and detection of a multibit, multiplicative watermark hosted by Weibull-distributed features: a situation which is classically encountered for image watermarking in the magnitude-of-DFT domain. As such, this work can be seen as an extension of the system described in a previous paper, where the same problem is addressed for the case of 1-bit watermarking. The theoretical analysis is validated through Monte Carlo simulations. Although the structure of the optimum decoder/detector is derived in the absence of attacks, some experimental results are also presented, giving a measure of the overall robustness of the watermark when attacks are present.

Image Forgery Localization via Fine-Grained Analysis of CFA Artifacts

In this paper, a forensic tool able to discriminate between original and forged regions in an image captured by a digital camera is presented. We make the assumption that the image is acquired using a Color Filter Array, and that tampering removes the artifacts due to the demosaicking algorithm. The proposed method is based on a new feature measuring the presence of demosaicking artifacts at a local level, and on a new statistical model allowing to derive the tampering probability of each 2 × 2 image block without requiring to know a priori the position of the forged region. Experimental results on different cameras equipped with different demosaicking algorithms demonstrate both the validity of the theoretical model and the effectiveness of our scheme.

Capacity of full frame DCT image watermarks

The evaluation of the number of bits that can be hidden within an image through digital watermarking is a crucial topic, which has been addressed only for additive watermarks. The evaluation of watermark capacity is very important because it allows to put a theoretical upper bound on the amount of information that can be hidden into an image by a given watermarking procedure, regardless of the watermark extraction technique. It is the purpose of this work to suggest a methodology for the evaluation of the watermark capacity in a nonadditive, non-Gaussian framework, and to discuss the results we obtained by applying it to a set of standard images.

Multispectral imaging of paintings

Identifying the materials of a painting is a crucial step in any conservation process. When the objective is to prepare an intervention plan, it is absolutely necessary to understand the matters the restorer is going to encounter. Also, when the aim is a better understanding of the artwork, and perhaps an authenticity check, it is highly relevant to know which materials were employed, since they may differ depending on the period of execution and on the specific artist as well. To identify materials on a paintings surface in a reliable manner, currently the most popular and trustworthy method is the analysis of microsamples of the paint layer. However, chemical analyses although reliable, have a number of drawbacks. The first is linked to the fact that this is an invasive method. The samples used need to be detached from the painting and will not be put back in place. Moreover, the achieved results are in principle - and often also in practice - valid only for that specific specimen and cannot generally be extended to neighboring areas.

A Framework for Decision Fusion in Image Forensics Based on Dempster–Shafer Theory of Evidence

In this work, we present a decision fusion strategy for image forensics. We define a framework that exploits information provided by available forensic tools to yield a global judgment about the authenticity of an image. Sources of information are modeled and fused using Dempster-Shafer Theory of Evidence, since this theory allows us to handle uncertain answers from tools and lack of knowledge about prior probabilities better than the classical Bayesian approach. The proposed framework permits us to exploit any available information about tools reliability and about the compatibility between the traces the forensic tools look for. The framework is easily extendable: new tools can be added incrementally with a little effort. Comparison with logical disjunction- and SVM-based fusion approaches shows an improvement in classification accuracy, particularly when strong generalization capabilities are needed.

A DWT-based object watermarking system for MPEG-4 video streams

The MPEG-4 standard is revealing very attractive for a large set of applications. In some of them a copy protection system allowing to control the distribution of multimedia data is required. A new technology useful for copyright protection is watermarking: a digital code (watermark), indicating the copyright owner, is directly embedded into the video signal. The possibility of the MPEG-4 standard to directly access objects within a video sequence introduces a constraint to the watermarking process: even if a video object is transferred from a sequence to another, the copyright data of the single object has to be correctly detected. Another requirement is that, in order to be robust against format conversions, the watermark has to be inserted before compression. The method proposed in this paper satisfies the previous requirements by relying on an image watermarking algorithm which embeds the code in the discrete wavelet transform of each frame.

Robust frame-based watermarking for digital video

Opening digital archives to the access of a large and spread variety of parties appears to depend on the development of more effective solutions for the transfer of rights, the protection of intellectual property and the access to digital libraries. A possible solution envisages the use of digital watermarking of multimedia works. In this paper a watermarking algorithm originally conceived for still images applications, is extended to raw video, treating it as a set of still frames. A good robustness against common image processing and geometric manipulations was achieved. Moreover, experiments with MPEG2 coding/decoding at different bit rates were carried out giving positive results.

Secure Client-Side ST-DM Watermark Embedding

Client-side watermark embedding systems have been proposed as a possible solution for the copyright protection in large-scale content distribution environments. In this framework, we propose a new look-up-table-based secure client-side embedding scheme properly designed for the spread transform dither modulation watermarking method. A theoretical analysis of the detector performance under the most known attack models is presented and the agreement between theoretical and experimental results verified through several simulations. The experimental results also prove that the advantages of the informed embedding technique in comparison to the spread-spectrum watermarking approach, which are well known in the classical embedding schemes, are preserved in the client-side scenario. The proposed approach permits us to successfully combine the security of client-side embedding with the robustness of informed embedding methods.

Copyright protection of cultural heritage multimedia data through digital watermarking techniques

Digital watermarking has been revealed to be an efficient technique to cope with the problem of intellectual property rights (IPR) protection of multimedia data. This technology embeds into the data an unperceivable digital code, namely the watermark, carrying information about the copyright status of the work to be protected. In this paper, the practical feasibility of IPR protection of multimedia data through digital watermarking is investigated. As it is shown, the effectiveness of watermarking as an IPR protection tool turns out to be heavily affected by the detection strategy, which has to be carefully matched to the application at hand. Finally the practical case of the Tuscany&Gifu Art Virtual Gallery has been considered in detail, to further explain in which manner a watermarking technique can be actually used.