This paper presents an efficient method for the estimation and recovering from nonlinear or local geometrical distortions, such as the random bending attack and restricted projective transforms. The distortions are modeled as a set of local affine transforms, the watermark being repeatedly allocated into small blocks in order to ensure its locality. The estimation of the affine transform parameters is formulated as a robust penalized Maximum Likelihood (ML) problem, which is suitable for the local level as well as for global distortions. Results with the Stirmark benchmark confirm the high robustness of the proposed method and show its state-of-the-art performance.

Digital watermarks have been proposed as a method for discouraging illicit copying and distribution of copyrighted material. This paper describes a method for the secure and robust copyright protection of digital images. We present an approach for embedding a digital watermark into an image using the fast Fourier transform. To this watermark is added a template in the Fourier transform domain to render the method robust against rotations and scaling, or aspect ratio changes. We detail a new algorithm based on the logpolar or log-log maps for the accurate and ecient recovery of the template in a rotated and scaled image. We also present results which demonstrate the robustness of the method against some common image processing operations such as compression, rotation, scaling and aspect ratio changes.

Digital watermarking appears today as an e cient mean of securing multimedia documents. Several application scenarios in the security of digital watermarking have been pointed out, each of them with di erent requirements. The three main identiÿed scenarios are: copyright protection, i.e. protecting ownership and usage rights; tamper prooÿng, aiming at detecting malicious modiÿcations; and authentication, the purpose of which is to check the authenticity of the originator of a document. While robust watermarks, which survive to any change or alteration of the protected documents, are typically used for copyright protection, tamper prooÿng and authentication generally require fragile or semi-fragile watermarks in order to detect modiÿed or faked documents. Further, most of robust watermarking schemes are vulnerable to the so-called copy attack, where a watermark can be copied from one document to another by any unauthorized person, making these schemes ine cient in all authentication applications. In this paper, we propose a hybrid watermarking method joining a robust and a fragile or semi-fragile watermark, and thus combining copyright protection and tamper prooÿng. As a result this approach is at the same time resistant against copy attack. In addition, the fragile information is inserted in a way which preserves robustness and reliability of the robust part. The numerous tests and the results obtained according to the Stirmark benchmark demonstrate the superior performance of the proposed approach. ?

This paper proposes a new approach for digital watermarking and secure copyright protection of videos, the principal aim being to discourage illicit copying and distribution of copyrighted material. The method presented here is based on the discrete Fourier transform (DFT) of three dimensional chunks of video scene, in contrast with previous works on video watermarking where each video frame was marked separately, or where only intra-frame or motion compensation parameters were marked in MPEG compressed videos. Two kinds of information are hidden in the video: a watermark and a template. Both are encoded using an owner key to ensure the system security and are embedded in the 3D DFT magnitude of video chunks. The watermark is a copyright information encoded in the form of a spread spectrum signal. The template is a key based grid and is used to detect and invert the eect of frame-rate changes, aspect-ratio modication and rescaling of frames. The template search and matching is performed in the log-log-log map of the 3D DFT magnitude. The performance of the presented technique is evaluated experimentally and compared with a frame-by-frame 2D DFT watermarking approach.

An important problem constraining the practical exploitation of robust watermarking technologies is the low robustness of the existing algorithms against geometrical distortions such as rotation, scaling, cropping, translation, change of aspect ratio and shearing. All these attacks can be uniquely described by general affine transforms. In this work, we propose a robust estimation method using apriori known regularity of a set of points. These points can be typically local maxima, or peaks, resulting either from the autocorrelation function (ACF) or from the magnitude spectrum (MS) generated by periodic patterns, which result in regularly aligned and equally spaced points. This structure is kept under any affine transform. The estimation of affine transform parameters is formulated as a robust penalized Maximum Likelihood (ML) problem. We propose an efficient approximation of this problem based on Hough transform (HT) or Radon transform (RT), which are known to be very robust in detecting alignments, even when noise is introduced by misalignments of points, missing points, or extra points. The high efficiency of the method is demonstrated even when severe degradations have occurred, including JPEG compression with a quality factor of 50%, where other known algorithms fail. Results with the Stirmark benchmark confirm the high robustness of the proposed method.