With the advent of sophisticated and low-cost video editing software, it is becoming increasingly easier to tamper with digital video. In addition, an ever-growing number of video surveillance cameras is giving rise to an enormous amount of video data. The ability to ensure the integrity and authenticity of this data poses considerable challenges. Here we begin to explore techniques for detecting traces of tampering in digital video. Specifically, we show how a doublycompressed MPEG video sequence introduces specific static and temporal statistical perturbations whose presence can be used as evidence of tampering. Categories and Subject Descriptors I.4 [Image Processing]: Miscellaneous General Terms Security Keywords Digital Tampering, Digital Forensics