Using PNU-based techniques to detect alien frames in videos

In this paper we discuss about video integrity problem and specifically we analyze whether the method proposed by Fridrich et al. [16] can be exploited for forensic purposes. In particular Fridrich et al. proposed a solution to identify the source camera given an input image. The method relies on the Pixel Non-Uniformity (PNU) noise produced by the sensor and existing in any digital image. We first present a wider scenario related to video integrity. Then we focus on a particular case of video forgery where sequences of frames, recorded by a different camera (in short, alien frames), could be added to the original video. By means of experimental evaluation in specific real world forensic scenarios we analyzed the accuracy degree that this method can achieve and we evaluated the critical conditions where the results are not enough reliable to be considered in courts. The results show that the method is robust, and alien frames can be reliably detected provided that the source device (or its faithful fingerprint) is available. Nevertheless the discussed method applies to a rather limited concept of video integrity (alien frames detection) and more extensive solutions, able to cover a wider range of application scenarios, would be required as well.