Digital image watermarking: its formal model, fundamental properties and possible attacks

While formal definitions and security proofs are well established in some fields like cryptography and steganography, they are not as evident in digital watermarking research. A systematic development of watermarking schemes is desirable, but at present their development is usually informal, ad hoc, and omits the complete realization of application scenarios. This practice not only hinders the choice and use of a suitable scheme for a watermarking application, but also leads to debate about the state-of-the-art for different watermarking applications. With a view to the systematic development of watermarking schemes, we present a formal generic model for digital image watermarking. Considering possible inputs, outputs, and component functions, the initial construction of a basic watermarking model is developed further to incorporate the use of keys. On the basis of our proposed model, fundamental watermarking properties are defined and their importance exemplified for different image applications. We also define a set of possible attacks using our model showing different winning scenarios depending on the adversary capabilities. It is envisaged that with a proper consideration of watermarking properties and adversary actions in different image applications, use of the proposed model would allow a unified treatment of all practically meaningful variants of watermarking schemes

The square root law of steganographic capacity.

There are a number of recent information theoretic results demonstrating (under certain conditions) a sublinear relationship between the number of cover objects and their total steganographic capacity. in this paper we explain how these results may be adapted to the steganographic capacity of a single cover object, which under the right conditions should be proportional to the square root of the cover size. Then we perform some experiments using three genuine steganography methods in digital images, covering both spatial and DOT domains. Measuring detectability under four different steganalysis methods, for a, variety of payload and cover sizes, we observe close accordance with a square root law. Copyright 2008 ACM

The square root law of steganographic capacity for Markov covers.

It is a well-established result that steganographic capacity of perfectly secure stegosystems grows linearly with the number of cover elements-secure steganography has a positive rate. In practice, however, neither the Warden nor the Steganographer has perfect knowledge of the cover source and thus it is unlikely that perfectly secure stegosystems for complex covers, such as digital media, will ever be constructed. This justifies study of secure capacity of imperfect stegosystems. Recent theoretical results from batch steganography, supported by experiments with blind steganalyzers, point to an emerging paradigm: whether steganography is performed in a large batch of cover objects or a single large object, there is a wide range of practical situations in which secure capacity rate is vanishing. In particular, the absolute size of secure payload appears to only grow with the square root of the cover size. In this paper, we study the square root law of steganographic capacity and give a formal proof of this law for imperfect stegosystems, assuming that the cover source is a stationary Markov chain and the embedding changes are mutually independent. © 2009 Copyright SPIE - The International Society for Optical Engineering

From Blind to Quantitative Steganalysis.

A quantitative steganalyzer is an estimator of the number of embedding changes introduced by a specific embedding operation. Since for most algorithms the number of embedding changes correlates with the message length, quantitative steganalyzers are important forensic tools. In this paper, a general method for constructing quantitative steganalyzers from features used in blind detectors is proposed. The core of the method is a support vector regression, which is used to learn the mapping between a feature vector extracted from the investigated object and the embedding change rate. To demonstrate the generality of the proposed approach, quantitative steganalyzers are constructed for a variety of steganographic algorithms in both JPEG transform and spatial domains. The estimation accuracy is investigated in detail and compares favorably with state-of-the-art quantitative steganalyzers. © 2006 IEEE

The square root law of steganographic capacity.

There are a number of recent information theoretic results demonstrating (under certain conditions) a sublinear relationship between the number of cover objects and their total steganographic capacity. in this paper we explain how these results may be adapted to the steganographic capacity of a single cover object, which under the right conditions should be proportional to the square root of the cover size. Then we perform some experiments using three genuine steganography methods in digital images, covering both spatial and DOT domains. Measuring detectability under four different steganalysis methods, for a, variety of payload and cover sizes, we observe close accordance with a square root law. Copyright 2008 ACM

Multimedia authentication and watermarking

Most multimedia signals today are in digital formats which are easy to reproduce and modify without any trace of manipulations. In this chapter, we present a comprehensive review of current technologies for multimedia data authentication and tamper detection. We first introduce in Section 7.2 the problem issues and general requirements for a multimedia authentication system. This is followed in Section 7.3 with detailed descriptions of the current algorithms for the three types of multimedia authentication: hard or complete authentication, soft authentication, and content-based authentication. The conclusion and future research directions are presented in Section 7.4

Artrocentese da articulação temporomandibular: avaliação de resultados e revisão da literatura Temporomandibular joint arthrocententesis: evaluation of results and review of the literature

OBJETIVO: Avaliar o efeito da artrocentese em relação à sintomatologia e movimentação mandibular em uma serie de pacientes com deslocamento anterior de disco e travamento mandibular. MATERIAIS E MÉTODOS: O estudo foi baseado nos dados pré e pós-operatório de pacientes através de exame clínico e radiográfico. A Escala Analógica Visual (EAV) foi usada para quantificar a dor no pré e pós-operatório. Foram avaliados 6 pacientes (12 articulações) tratados no Hospital Universitário Oswaldo Cruz (HUOC) com travamento mandibular (2 casos) e desarranjo interno (4 casos). O período médio de acompanhamento foi de 11,5 meses. RESULTADOS: A média de abertura bucal pré-operatória foi de 31,83mm e no pós-operatório foi de 36,50mm. A média de dor articular segundo a escala visual analógica encontrada foi de 7 e no pós-operatório foi de 4,3. CONCLUSÃO: A artrocentese mostrou-se efetiva na melhora da dor articular e na movimentação mandibular nesta série de casos.<br>AIM: This study was designed to investigate the effects of arthrocentesis on the improvement of internal derangement symptoms and jaw function in a series of patients with anterior disc displacement and closed lockjaw. PATIENTS AND METHODS: The study was based on a review of patients’ records before and after treatment using clinical examinations and radiographs. Visual analog scales were used to measure pain before and after arthrocentesis. Six patients (12 temporomandibular joints) with closed lock symptoms (2 cases) and internal derangements (4 cases) were treated at the Oswaldo Cruz Hospital. The mean follow-up was 11.5 months. RESULTS: The mean maximum vertical opening before treatment was 31.83 mm and after arthrocentesis was 36.50 mm. The visual analog scale for pain before treatment was 7 points (mean) and after arthrocentesis the mean was 4.3. CONCLUSION: Arthrocentesis was shown to be effective in reducing pain and increasing jaw motion in this series of cases