UMD Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/3
New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a given thesis/dissertation in DRUM.
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Item Intrinsically Embedded Signatures for Multimedia Forensics(2016) Al Hajj Ahmad, Adi Mohammad; Wu, Min; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation examines the use of signatures that are intrinsically embedded in media recordings for studies and applications in multimedia forensics. These near-invisible signatures are fingerprints that are captured unintentionally in a recording due to influences from the environment in which it was made and the recording device that was used to make it. We focus on two types of such signatures: the Electric Network Frequency (ENF) signal and the flicker signal. The ENF is the frequency of power distribution networks and has a nominal value of 50Hz or 60Hz. The ENF fluctuates around its nominal value due to load changes in the grid. It is particularly relevant to multimedia forensics because ENF variations captured intrinsically in a media recording reflect the time and location related properties of the respective area in which it was made. This has led to a number of applications in information forensics and security, such as time-of-recording authentication/estimation and ENF-based detection of tampering in a recording. The first part of this dissertation considers the extraction and detection of the ENF signal. We discuss our proposed spectrum combining approach for ENF estimation that exploits the presence of ENF traces at several harmonics within the same recording to produce more accurate and robust ENF signal estimates. We also explore possible factors that can promote or hinder the capture of ENF traces in recordings, which is important for a better understanding of the real-world applicability of ENF signals. Next, we discuss novel real-world ENF-based applications proposed through this dissertation research. We discuss using the embedded ENF signal to identify the region-of-recording of a media signal through a pattern analysis and learning framework that distinguishes between ENF signals coming from different power grids. We also discuss the use of the ENF traces embedded in a video to characterize the video camera that had originally produced the video, an application that was inspired by our work on flicker forensics. The last part of the dissertation considers the flicker signal and its use in forensics. We address problems in the entertainment industry pertaining to movie piracy related investigations, where a pirated movie is formed by camcording media content shown on an LCD screen. The flicker signature can be inherently created in such a scenario due to the interplay between the back-light of an LCD screen and the recording mechanism of the video camera. We build an analytic model of the flicker, relating it to inner parameters of the video camera and the screen producing the video. We then demonstrate that solely analyzing such a pirated video can lead to the identification of the video camera and the screen that produced the video, which can be used as corroborating evidence in piracy investigations.Item Fundamental Limits in Multimedia Forensics and Anti-forensics(2015) Chu, Xiaoyu; Liu, K. J. Ray; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)As the use of multimedia editing tools increases, people become questioning the authenticity of multimedia content. This is specially a big concern for authorities, such as law enforcement, news reporter and government, who constantly use multimedia evidence to make critical decisions. To verify the authenticity of multimedia content, many forensic techniques have been proposed to identify the processing history of multimedia content under question. However, as new technologies emerge and more complicated scenarios are considered, the limitation of multimedia forensics has been gradually realized by forensic researchers. It is the inevitable trend in multimedia forensics to explore the fundamental limits. In this dissertation, we propose several theoretical frameworks to study the fundamental limits in various forensic problems. Specifically, we begin by developing empirical forensic techniques to deal with the limitation of existing techniques due to the emergence of new technology, compressive sensing. Then, we go one step further to explore the fundamental limit of forensic performance. Two types of forensic problems have been examined. In operation forensics, we propose an information theoretical framework and define forensicability as the maximum information features contain about hypotheses of processing histories. Based on this framework, we have found the maximum number of JPEG compressions one can detect. In order forensics, an information theoretical criterion is proposed to determine when we can and cannot detect the order of manipulation operations that have been applied on multimedia content. Additionally, we have examined the fundamental tradeoffs in multimedia antiforensics, where attacking techniques are developed by forgers to conceal manipulation fingerprints and confuse forensic investigations. In this field, we have defined concealability as the effectiveness of anti-forensics concealing manipulation fingerprints. Then, a tradeoff between concealability, rate and distortion is proposed and characterized for compression anti-forensics, which provides us valuable insights of how forgers may behave under their best strategy.Item TIME AND LOCATION FORENSICS FOR MULTIMEDIA(2013) Garg, Ravi; Wu, Min; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In the modern era, a vast quantities of digital information is available in the form of audio, image, video, and other sensor recordings. These recordings may contain metadata describing important information such as the time and the location of recording. As the stored information can be easily modified using readily available digital editing software, determining the authenticity of a recording has utmost importance, especially for critical applications such as law enforcement, journalism, and national and business intelligence. In this dissertation, we study novel environmental signatures induced by power networks, which are known as Electrical Network Frequency (ENF) signals and become embedded in multimedia data at the time of recording. ENF fluctuates slightly over time from its nominal value of 50 Hz/60 Hz. The major trend of fluctuations in the ENF remains consistent across the entire power grid, including when measured at physically distant geographical locations. We investigate the use of ENF signals for a variety of applications such as estimation/verification of time and location of a recording's creation, and develop a theoretical foundation to support ENF based forensic analysis. In the first part of the dissertation, the presence of ENF signals in visual recordings captured in electric powered lighting environments is demonstrated. The source of ENF signals in visual recordings is shown to be the invisible flickering of indoor lighting sources such as fluorescent and incandescent lamps. The techniques to extract ENF signals from recordings demonstrate that a high correlation is observed between the ENF fluctuations obtained from indoor lighting and that from the power mains supply recorded at the same time. Applications of the ENF signal analysis to tampering detection of surveillance video recordings, and forensic binding of the audio and visual track of a video are also discussed. In the following part, an analytical model is developed to gain an understanding of the behavior of ENF signals. It is demonstrated that ENF signals can be modeled using a time-varying autoregressive process. The performance of the proposed model is evaluated for a timestamp verification application. Based on this model, an improved algorithm for ENF matching between a reference signal and a query signal is provided. It is shown that the proposed approach provides an improved matching performance as compared to the case when matching is performed directly on ENF signals. Another application of the proposed model in learning the power grid characteristics is also explicated. These characteristics are learnt by using the modeling parameters as features to train a classifier to determine the creation location of a recording among candidate grid-regions. The last part of the dissertation demonstrates that differences exist between ENF signals recorded in the same grid-region at the same time. These differences can be extracted using a suitable filter mechanism and follow a relationship with the distance between different locations. Based on this observation, two localization protocols are developed to identify the location of a recording within the same grid-region, using ENF signals captured at anchor locations. Localization accuracy of the proposed protocols are then compared. Challenges in using the proposed technique to estimate the creation location of multimedia recordings within the same grid, along with efficient and resilient trilateration strategies in the presence of outliers and malicious anchors, are also discussed.