Digital watermarking, information embedding, and data hiding systems

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2000.Includes bibliographical references (p. 139-142).Digital watermarking, information embedding, and data hiding systems embed information, sometimes called a digital watermark, inside a host signal, which is typically an image, audio signal, or video signal. The host signal is not degraded unacceptably in the process, and one can recover the watermark even if the composite host and watermark signal undergo a variety of corruptions and attacks as long as these corruptions do not unacceptably degrade the host signal. These systems play an important role in meeting at least three major challenges that result from the widespread use of digital communication networks to disseminate multimedia content: (1) the relative ease with which one can generate perfect copies of digital signals creates a need for copyright protection mechanisms, (2) the relative ease with which one can alter digital signals creates a need for authentication and tamper-detection methods, and (3) the increase in sheer volume of transmitted data creates a demand for bandwidth-efficient methods to either backwards-compatibly increase capacities of existing legacy networks or deploy new networks backwards-compatibly with legacy networks. We introduce a framework within which to design and analyze digital watermarking and information embedding systems. In this framework performance is characterized by achievable rate-distortion-robustness trade-offs, and this framework leads quite naturally to a new class of embedding methods called quantization index modulation (QIM). These QIM methods, especially when combined with postprocessing called distortion compensation, achieve provably better rate-distortion-robustness performance than previously proposed classes of methods such as spread spectrum methods and generalized low-bit modulation methods in a number of different scenarios, which include both intentional and unintentional attacks. Indeed, we show that distortion-compensated QIM methods can achieve capacity, the information-theoretically best possible rate-distortion-robustness performance, against both additive Gaussian noise attacks and arbitrary squared error distortion-constrained attacks. These results also have implications for the problem of communicating over broadcast channels. We also present practical implementations of QIM methods called dither modulation and demonstrate their performance both analytically and through empirical simulations.by Brian Chen.Ph.D

Adaptive OFDM Radar for Target Detection and Tracking

We develop algorithms to detect and track targets by employing a wideband orthogonal frequency division multiplexing: OFDM) radar signal. The frequency diversity of the OFDM signal improves the sensing performance since the scattering centers of a target resonate variably at different frequencies. In addition, being a wideband signal, OFDM improves the range resolution and provides spectral efficiency. We first design the spectrum of the OFDM signal to improve the radar\u27s wideband ambiguity function. Our designed waveform enhances the range resolution and motivates us to use adaptive OFDM waveform in specific problems, such as the detection and tracking of targets. We develop methods for detecting a moving target in the presence of multipath, which exist, for example, in urban environments. We exploit the multipath reflections by utilizing different Doppler shifts. We analytically evaluate the asymptotic performance of the detector and adaptively design the OFDM waveform, by maximizing the noncentrality-parameter expression, to further improve the detection performance. Next, we transform the detection problem into the task of a sparse-signal estimation by making use of the sparsity of multiple paths. We propose an efficient sparse-recovery algorithm by employing a collection of multiple small Dantzig selectors, and analytically compute the reconstruction performance in terms of the $ell_1$-constrained minimal singular value. We solve a constrained multi-objective optimization algorithm to design the OFDM waveform and infer that the resultant signal-energy distribution is in proportion to the distribution of the target energy across different subcarriers. Then, we develop tracking methods for both a single and multiple targets. We propose an tracking method for a low-grazing angle target by realistically modeling different physical and statistical effects, such as the meteorological conditions in the troposphere, curved surface of the earth, and roughness of the sea-surface. To further enhance the tracking performance, we integrate a maximum mutual information based waveform design technique into the tracker. To track multiple targets, we exploit the inherent sparsity on the delay-Doppler plane to develop an computationally efficient procedure. For computational efficiency, we use more prior information to dynamically partition a small portion of the delay-Doppler plane. We utilize the block-sparsity property to propose a block version of the CoSaMP algorithm in the tracking filter

Digitale Wasserzeichenverfahren zur Überprüfung der Echtheit von Bildern

Die Dissertation liefert einen Beitrag zur Entwicklung von Wasserzeichensystemen zur manipulationssicheren Überprüfung der Echtheit von Bildern. In den Prozess einer JPEG2000-Bildkompression integriert wird ein an den Bildinhalt angepasstes Wasserzeichen nicht-wahrnehmbar ein­gebettet. Es ist robust gegenüber einer breiten Auswahl erlaubter Bildoperatio­nen, wie Kompression des Bildes, Helligkeits- und Kontrastände­rungen, Filterung, Bildschärfun­g sowie Skalierung der Bildgröße. Die Arbeit beinhaltet zudem umfangreiche Untersuchungen, Erweiterungen und Vergleiche mit Verfahren anderer Autoren

Digitale Wasserzeichenverfahren zur Überprüfung der Echtheit von Bildern

Die Dissertation liefert einen Beitrag zur Entwicklung von Wasserzeichensystemen zur manipulationssicheren Überprüfung der Echtheit von Bildern. In den Prozess einer JPEG2000-Bildkompression integriert wird ein an den Bildinhalt angepasstes Wasserzeichen nicht-wahrnehmbar ein­gebettet. Es ist robust gegenüber einer breiten Auswahl erlaubter Bildoperatio­nen, wie Kompression des Bildes, Helligkeits- und Kontrastände­rungen, Filterung, Bildschärfun­g sowie Skalierung der Bildgröße. Die Arbeit beinhaltet zudem umfangreiche Untersuchungen, Erweiterungen und Vergleiche mit Verfahren anderer Autoren