Monitoring mechanical properties of structures such as bridges, buildings, or wind turbines, is important to detect early stage failures. Operational modal analysis is a testing method to estimate these properties from vibration measurements. Taking advantage of works on motion estimation, several video modal analysis methods have emerged in the last decade. This paper compares two strategies about sub-pixel phase-based motion estimations thanks to multi-scale decomposition. Synthetic videos of a vibrating cantilever beam are generated to assess the robustness of these methods against motion amplitude, gray scale quantization, white noise, and blurring.

This paper studies the impact of secure watermark embedding in digital images by proposing a practical implementation of secure spread-spectrum watermarking using distortion optimization. Because strong security properties (key-security and subspace-security) can be achieved using natural watermarking (NW) since this particular embedding lets the distribution of the host and watermarked signals unchanged, we use elements of transportation theory to minimize the global distortion. Next, we apply this new modulation, called transportation NW (TNW), to design a secure watermarking scheme for grayscale images. The TNW uses a multiresolution image decomposition combined with a multiplicative embedding which is taken into account at the distribution level. We show that the distortion solely relies on the variance of the wavelet subbands used during the embedding. In order to maximize a target robustness after JPEG compression, we select different combinations of subbands offering the lowest Bit Error Rates for a target PSNR ranging from 35 to 55 dB and we propose an algorithm to select them. The use of transportation theory also provides an average PSNR gain of 3.6 dB on PSNR with respect to the previous embedding for a set of 2000 images.

This paper presents a moderately secure but very efficient approximate nearest neighbors search. After detailing the threats pertaining to the `honest but curious' model, our approach starts from a state-of-the-art algorithm in the domain of approximate nearest neighbors search. We gradually develop mechanisms partially blocking the attacks threatening the original algorithm.

This paper presents a study of the embedding of Tardos binary fingerprinting codes with watermarking techniques. By taking into account the security of the embedding scheme, we present a new approach for colluding strategies which relies on the possible estimation error rate of the code symbols (denoted$\epsilon$). We derive a new attack strategy called “$\epsilon$-Worst Case Attack” and show its efficiency using the computation of achievable rates for simple decoding. Then we consider the interplay between security and robustness regarding the accusation performances of the fingerprinting scheme and show that 1) for the same accusation rate secure schemes can afford to be less robust than insecure ones, and 2) that secure schemes enable to cast the Worst Case Attack into an interleaving attack. Additionally, we use the security analysis of the watermarking scheme to derive from$\epsilon$a security attack for a fingerprinting scheme based on Tardos codes and a new scheme called stochastic spread-spectrum watermarking. We compare a removal attack against an AWGN robustness attack and we show that for the same distortion, the combination of a fingerprinting attack and a security attack easily outperform classical attacks even with a small number of observations.

This article is a theoretical study on binary Tardos' fingerprinting codes embedded using watermarking schemes. Our approach is derived from and encompasses both security and robustness constraints. We assume here that the coalition has estimated the symbols of the fingerprinting code by the way of a security attack, the quality of the estimation relying on the security of the watermarking scheme. Taking into account the fact that the coalition can perform estimation errors, we update the Worst Case Attack, which minimises the mutual information between the sequence of one colluder and the pirated sequence forged by the coalition. After comparing the achievable rates of the previous and proposed Worst Case Attack according to the estimation error, we conclude this analysis by comparing the robustness of no-secure embedding schemes versus secure ones. We show that, for low probabilities of error during the decoding stage (e.g. highly robust watermarking schemes), security enables to increase the achievable rate of the fingerprinting scheme.