Forensic Examination of CCTV Digital VTR Surveillance Recording Equipment

Approximately two years ago I authored a paper entitled, “The Forensic Examination of Video Recordings” which discussed some of the more conventional forensic techniques for examining questioned analog videotapes regarding their originality and for possible evidence of tape alteration. This paper specifically addressed the various mechanical and electrical signal anomalies that occur when editing of videotape is present or if different analog VCR ‘s had been used in the production of composite videotapes. The videotapes examined included conventional two-hour VHS which were continuously recorded on the original VCR. The instruments utilized in the examination of these continuously recorded two-hour videotapes included an oscilloscope, a waveform monitor, cross pulse monitor, spectrum analyzer, and other analytical equipment. Whenever editing/tampering did occur on a evidential videotape, invariably the above listed equipment was successful in identifying various timing differences that produced visible variations in the horizontal, vertical, and color synchronization pulses which makeup the video waveform. Portions of the audio signal are also often adversely affected because of the editing process. This paper will focus on the operational characteristics of both analog and digital CCTV time lapse VCR’s and the forensic tools utilized in their testing and evaluation. (1)