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In the wake of widespread surfeit of inexpensive and user-friendly digital multimedia alteration software, digital images and videos have lost the unparalleled position they once occupied as 'authoritative testament of occurrence of events'. The inherent susceptibility of digital content to malevolent manipulations renders it vulnerable to our skepticism. Establishment of authenticity of digital content is of utmost importance in situations where reliability on fraudulent evidence could have serious consequences.With the intent of tackling a few of the several challenges of the video forensics domain, in this paper we propose a potent DCT coefficient analysis-based forensic technique for reliable detection of re-compression and transcoding in digital videos. This scheme facilitates visually perceptible differentiation between singly-compressed and re-compressed video frames while circumventing the need for undertaking any complicated peak periodicity analysis procedures that are normally associated with traditional DCT-based studies. We also present a unique optical-flow analysis scheme, where, instead of inspecting inconsistencies caused by frame-removal in the entire optical flow sequences of a given video, we focus entirely on the brightness gradient component of this flow. The experiments in this regard substantiate the forensic capabilities of this component and proffer observations conducive to the detection and localization of frame-removal in digital videos. Subjective and quantitative experimentation on a comprehensive dataset under a wide range of experimental set-ups validate the efficacy and resilience of the proposed techniques.

In the wake of widespread proliferation of inexpensive and easy-to-use digital content editing software, digital videos have lost the idealized reputation they once held as universal, objective and infallible evidence of occurrence of events. The pliability of digital content and its innate vulnerability to unobtrusive alterations causes us to become skeptical of its validity. However, in spite of the fact that digital videos may not always present a truthful picture of reality, their usefulness in today’s world is incontrovertible. Therefore, the need to verify the integrity and authenticity of the contents of a digital video becomes paramount, especially in critical scenarios such as defense planning and legal trials where reliance on untrustworthy evidence could have grievous ramifications. Inter-frame tampering, which involves insertion/removal/replication of sets of frames into/from/within a video sequence, is among the most un-convoluted and elusive video forgeries. In this paper, we propose a potent hybrid forensic system that detects inter-frame forgeries in compressed videos. The system encompasses two forensic techniques. The first is a novel optical flow analysis based frame-insertion and removal detection procedure, where we focus on the brightness gradient component of optical flow and detect irregularities caused therein by post-production frame-tampering. The second component is a prediction residual examination based scheme that expedites detection and localization of replicated frames in video sequences. Subjective and quantitative results of comprehensive tests on an elaborate dataset under diverse experimental set-ups substantiate the effectuality and robustness of the proposed system.

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