| dc.description.abstract | The purpose of this research is to develop a forensic scheme to determine whether an investigated video has been tampered by editing processes, including shot deletion, replacement or insertion, and so on. A detection mechanism based on H.264/AVC de-blocking filter is proposed. Considering that the original video is encoded with H.264/AVC and so is the investigated video, when certain shots in the original encoded video is edited, the re-encoding, may make some I frames in the original GOP (Group of Pictures) be converted into P frames. Such abnormal coding information generated by the tampering operations is employed to assess the authenticity of the investigated video.
Most of the proposed tampering detection methods utilize the information of the coding residuals. This study makes use of the de-blocking filter related information in H.264/AVC, which is more difficult to be attacked by anti-detection method than the existing methods. We extract the Boundary Strength (BS), which is the basis of the de-blocking filter for evaluating the filter strength of 4x4 block boundaries. Two graphs for analysis are formed, i.e., Prediction Residual Graph (PRG) and Inter-Prediction Graph (IPG) in a two-dimensional image. In order to deal with various kinds of anti-detection or tampering operations, the proposed method defines three kinds of discontinuities by analyzing PRG or IPG. Three evaluation methods are thus developed, including (1) VRF (Variation of Residual Footprint), which operates on PRG to improve the existing VPF (Variation of Prediction Footprint), (2) DOF (Degree of Fragments), which processes IPG and (3) VCF (Variation of Centroid Footprint), which calculates the offset of centroid in PRG. Finally, we estimate the distances between the detected peaks and find the distance that occurs most frequently to acquire the original GOP size, followed by the determination of the editing position. Besides, the latest anti-detection technology, an attacking method based on changing the quantized coefficients, is also used to verify the proposed detection mechanism based on the de-blocking filter. Experimental results show that, no matter using the fixed QP (Quantization Parameter) or CBR (Constant Bit Rate) encoding, the video after anti-detection attack still reveals abnormal phenomena, which demonstrate the robustness of the proposed method. | en_US |