Perceptual hashing has to deal with the constraints of robustness, accuracy and security. After modeling the
process of hash extraction and the properties involved in this process, two different security threats are studied,
namely the disclosure of the secret feature space and the tampering of the hash. Two different approaches for
performing robust hashing are presented: Random-Based Hash (RBH) where the security is achieved using a
random projection matrix and Content-Based Hash (CBH) were the security relies on the difficulty to tamper the
hash. As for digital watermarking, different security setups are also devised: the Batch Hash Attack, the Group
Hash Attack, the Unique Hash Attack and the Sensitivity Attack. A theoretical analysis of the information
leakage in the context of Random-Based Hash is proposed. Finally, practical attacks are presented: (1) Minor
Component Analysis is used to estimate the secret projection of Random-Based Hashes and (2) Salient point
tampering is used to tamper the hash of Content-Based Hashes systems.
KEYWORDS: Data hiding, Signal to noise ratio, Signal detection, Interference (communication), Electronic filtering, Distortion, Digital watermarking, Sensors, Coding theory, Signal analyzers
This paper deals with the problem of synchronization in the particular case of audio data hiding. In this kind of application the goal is to increase the information of an audio data set by inserting an imperceptible message. An innovating synchronization scheme that uses informed coding theory is proposed. The goal is to realize a complementary approach from two different techniques in order to obtain an enhanced synchronization system. To that end, the analysis of the classical spread spectrum synchronization is done and this classical scheme is improved by the use of side information. Informed coding theory is presented and revisited taking into account the problem of synchronization to enable the selection of signal realizations called Feature Time Points (FTP) which are correlated with a code. Such considerations yield to the definition of informed synchronization. The proposed scheme and the definition of FTP are after presented taking into account the robustness criterion. Finally, results and comparison with classical spread spectrum synchronization schemes are presented.
Watermarking techniques have been considerably improved for the last past years, aiming at being always more resistant to attacks. In fact, if the main goal of watermarking at the beginning was to secure digital data (audio, image and video), numerous attacks are still now able to cast doubts on the owner's authenticity ; we can distinguish three different groups of attacks : these one which consist to remove the watermark, these one which aim at impairing the data sufficiently to falsify the detection, and finally these one which try to alter the detection process so that another person becomes the apparent owner of the data.
By considering the growing development of always more efficient attacks, this paper firstly presents a recent and exhaustive review of attacks in image and video watermarking. In a second part, the consequences of still image watermarking attacks on video sequences will be outlined and a particular attention will be given to the recently created benchmarks : Stirmark, the benchmark proposed by the University of Geneva Vision Group, this one proposed by the Department of Informatics of the University of Thessaloniki and finally we will speak of the current work of the European Project Certimark ; we will present a comparison of these various benchmarks and show how difficult it is to develop a self-sufficient benchmark, especially because of the complexity of intentional attacks.
KEYWORDS: Digital watermarking, Video, Signal detection, Optical correlators, Principal component analysis, Binary data, Video processing, Video compression, Multimedia, Signal processing
This paper presents two different watermarking schemes devoted to protect video objects. The first presented scheme performs embedding and detection in the uncompressed domain. It has been developed to enable signature detection after object manipulations such as rotations, translations and VOL modifications. To achieve these requirements, the first scheme exploits the shape of the object using CPA analysis: a random sequence is transformed to fit the scale and the orientation of the object. The detection of the mark is performed applying an inverse transform and calculating a correlation between the random sequence and the transformed object. The second scheme is based on compressed-domain processing of video objects. Two different signals are embedded, one for synchronization recovery and another for copyright protection. Both signals are embedded and detected in the compressed domain. During detection, first synchronization recovery is performed and then the copyright watermark is extracted.
Numerical information is volatile and watermarking is a solution to assist copyright protection. During the detection step, the synchronization of the mark is a great problem. Geometric transformations can defeat the detector of the mark by desynchronizing the mark. Our scheme is based on warping of pre-defined triangular patterns. The content of the image (feature points) is used to mark independently different regions. This allows the synchronization of the mark for the detection step. Feature points mixed with a Delaunay tessellation permits to mark each triangle of the image. The detection is performed by warping triangle to a reference pattern and correlating with a reference triangle. Different algorithms have been developed in the spatial domain and in the frequential (DCT) domain. Our results show that our schemes are robust to Stirmark and other geometric transformations on different categories of images.
Watermarking schemes are more and more robust to classical degradations. The NEC system developed by Cox, using both original and marked images, can detect the mark with a JPEG compression ratio of 30. Nevertheless a very simple geometric attack done by the program Stirmark can remove the watermark. Most of the present watermarking schemes only map a mark on the image without geometric reference and therefore are not robust to geometric transformation. We present a scheme based on the modification of a collage map (issued from a fractal code used in fractal compression). We add a mark introducing similarities in the image. The embedding of the mark is done by selection of points of interest supporting blocks on which similarities are hided. This selection is done by the Stephens-Harris detector. The similarity is embedded locally to be robust to cropping. Contrary to many schemes, the reference mark used for the detection comes from the marked image and thus undergoes geometrical distortions. The detection of the mark is done by searching interest blocks and their similarities. It does not use the original image and the robustness is guaranteed by a key. Our first results show that the similarities-based watermarking is quite robust to geometric transformation such as translations, rotations and cropping.
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