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18 March 2008 In-theater piracy: finding where the pirate was
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Pirate copies of feature films are proliferating on the Internet. DVD rip or screener recording methods involve the duplication of officially distributed media whereas 'cam' versions are illicitly captured with handheld camcorders in movie theaters. Several, complementary, multimedia forensic techniques such as copy identification, forensic tracking marks or sensor forensics can deter those clandestine recordings. In the case of camcorder capture in a theater, the image is often geometrically distorted, the main artifact being the trapezoidal effect, also known as 'keystoning', due to a capture viewing axis not being perpendicular to the screen. In this paper we propose to analyze the geometric distortions in a pirate copy to determine the camcorder viewing angle to the screen perpendicular and derive the approximate position of the pirate in the theater. The problem is first of all geometrically defined, by describing the general projection and capture setup, and by identifying unknown parameters and estimates. The estimation approach based on the identification of an eight-parameter homographic model of the 'keystoning' effect is then presented. A validation experiment based on ground truth collected in a real movie theater is reported, and the accuracy of the proposed method is assessed.
© (2008) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Bertrand Chupeau, Ayoub Massoudi, and Frédéric Lefèbvre "In-theater piracy: finding where the pirate was", Proc. SPIE 6819, Security, Forensics, Steganography, and Watermarking of Multimedia Contents X, 68190T (18 March 2008);


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