Gwenaël J. Doërr

A guide tour of video watermarking

Digital watermarking was introduced at the end of the 20th century to provide means of enforcing copyright protection once the use and distribution of digital multimedia data have exploded. This technology has first been intensively investigated for still images and recent efforts have been put to exhibit unifying characteristics. On the other hand, the situation is rather different in the context of video watermarking, where unrelated articles are scattered throughout the literature. The purpose of this paper is consequently to give an in-depth overview of video watermarking and to point out that it is not only a simple extension of still images watermarking. New applications have to be considered, specific challenges have to be taken up and video-driven approaches have to be investigated.

Applying informed coding and embedding to design a robust high-capacity watermark

We describe a new watermarking system based on the principles of informed coding and informed embedding. This system is capable of embedding 1380 bits of information in images with dimensions 240/spl times/368 pixels. Experiments on 2000 images indicate the watermarks are robust to significant valumetric distortions, including additive noise, low-pass filtering, changes in contrast, and lossy compression. Our system encodes watermark messages with a modified trellis code in which a given message may be represented by a variety of different signals, with the embedded signal selected according to the cover image. The signal is embedded by an iterative method that seeks to ensure the message will not be confused with other messages, even after addition of noise. Fidelity is improved by the incorporation of perceptual shaping into the embedding process. We show that each of these three components improves performance substantially.

Security pitfalls of frame-by-frame approaches to video watermarking

Watermarking digital video material is usually considered as watermarking a sequence of still images. However, such a frame-by-frame approach is very risky since straightforward embedding strategies can result in poor performance in terms of security i.e., against hostile attacks. As examples, two very common video-watermarking systems will be presented as well as the associated intra-video collusion attacks which defeat them. Then, both watermark modulation and embedding strength modulation will be surveyed to design alternative embedding strategies which exhibit superior performance against such attacks. Nevertheless, it will also be shown that an expert attacker can still construct an effective watermark removal attack. Finally, there will be a discussion to assert whether or not security against intra-video collusion can be achieved with such blind frame-by-frame embedding strategies.

Still-image watermarking robust to local geometric distortions

Geometrical distortions are the Achilles heel for many watermarking schemes. Most countermeasures proposed in the literature only address the problem of global affine transforms (e.g., rotation, scaling, and translation). In this paper, we propose an original blind watermarking algorithm robust to local geometrical distortions such as the deformations induced by Stirmark. Our method consists in adding a predefined additional information to the useful message bits at the insertion step. These additional bits are labeled as resynchronization bits or reference bits and they are modulated in the same way as the information bits. During the extraction step, the reference bits are used as anchor points to estimate and compensate for small local and global geometrical distortions. The deformations are approximated using a modified basic optical flow algorithm

Toward generic image dewatermarking

During the last decade, a significant effort has been put into designing watermarking algorithms. The watermarking community now needs some advanced attacks and fair benchmarks in order to compare the performances of different watermarking technologies. Moreover, attacks permit the weaknesses of an algorithm to be found and consequently trigger further research in order to overcome the problem. These ideas motivated the creation of the European Certimark project. After a short definition of dewatermarking, we present an original attack based on self similarities. This attack is then put to the test with three different publicly available watermarking tools. Finally, we discuss briefly the feasibility of a generic attack i.e. a dewatermarking attack which should succeed in removing whatever watermarks have been inserted by whatever watermarking tools.

Secure background watermarking based on video mosaicing

Digital watermarking was introduced during the last decade as a complementary technology to protect digital multimedia data. Watermarking digital video material has already been studied, but it is still usually regarded as watermarking a sequence of still images. However, it is well-known that such straightforward frame-by-frame approaches result in low performance in terms of security. In particular, basic intra-video collusion attacks can easily defeat basic embedding strategies. In this paper, an extension of the simple temporal frame averaging attack will be presented, which basically considers frame registration to enlarge the averaging temporal window size. With this attack in mind, video processing, especially video mosaicing, will be considered to produce a temporally coherent watermark. In other words, an embedding strategy will be proposed which ensures that all the projections of a given 3D point in a movie set carry the same watermark sample along a video scene. Finally, there will be a discussion regarding the impact of this novel embedding strategy on different relevant parameters in digital watermarking e.g. capacity, visibility, robustness and security.

New intra-video collusion attack using mosaicing

Recent efforts for watermarking digital video extend the results obtained for still image watermarking. As a result, most of the proposed algorithms rely on a frame-by-frame approach. Such an adaptation leads to unreliable algorithms in terms of security. The goal of this article is to stress the problem of collusion when digital watermarked data is distributed at large scale and especially intra-video collusion in the context of video. Three simple collusion attacks are described before being evaluated on two alternative video watermarking algorithms based on the spread spectrum technique. Finally, some experimental results are presented confirming the danger of intra-video collusion and some perspectives are discussed.

Danger of low-dimensional watermarking subspaces

The security issue has been neglected for a long time in digital watermarking. Recent results for video watermarking have pointed out that existing watermarking schemes are not secure, i.e., a hostile intelligence succeeds in removing the hidden watermarks. In particular, for a given secret key, many watermarking schemes embed watermarks which lie in the same low-dimensional subspace whatever the host data is. We show that this subspace can be quite easily estimated with an efficient principal component analysis (PCA). For storage convenience, an online expectation-maximization (EM) algorithm is considered. Once this watermarking subspace has been estimated, an attacker only has to project incoming data onto the orthogonal of this subspace to remove the watermark.

Exploiting self-similarities to defeat digital watermarking systems: a case study on still images

Unauthorized digital copying is a major concern for multi-media content providers. Since copyright owners lose control over content distribution as soon as data is decrypted or unscrambled, digital watermarking has been introduced as a complementary protection technology. In an effort to anticipate hostile behaviors of adversaries, the research community is constantly introducing novel attacks to benchmark watermarking systems. In this paper, a generic block replacement attack will be presented. The underlying assumption is that multimedia content is highly repetitive. It should consequently be possible to exploit the self-similarities of the signal to replace each signal block with another perceptually similar one. Alternative methods to compute such a valid placement block will be surveyed in this paper. Then,experimental results on still images will be presented to the efficiency of the presented attack in comparison with other reference image processing operations. Finally, a will be conducted to exhibit the properties that a watermark should have to resist to this attack.

Collusion issue in video watermarking

Digital watermarking has first been introduced as a possible way to ensure intellectual property (IP) protection. However, fifteen years after its infancy, it is still viewed as a young technology and digital watermarking is far from being introduced in Digital Right Management (DRM) frameworks. A possible explanation is that the research community has so far mainly focused on the robustness of the embedded watermark and has almost ignored security aspects. For IP protection applications such as fingerprinting and copyright protection, the watermark should provide means to ensure some kind of trust in a non secure environment. To this end, security against attacks from malicious users has to be considered. This paper will focus on collusion attacks to evaluate security in the context of video watermarking. In particular, security pitfalls will be exhibited when frame-by-frame embedding strategies are enforced for video watermarking. Two alternative strategies will be surveyed: either eavesdropping the watermarking channel to identify some redundant hidden structure, or jamming the watermarking channel to wash out the embedded watermark signal. Finally, the need for a new brand of watermarking schemes will be highlighted if the watermark is to be released in a hostile environment, which is typically the case for IP protection applications.