"Seeing" ENF: natural time stamp for digital video via optical sensing and signal processing

Title"Seeing" ENF: natural time stamp for digital video via optical sensing and signal processing
Publication TypeConference Papers
Year of Publication2011
AuthorsGarg R, Varna AL, M. Wu
Conference NameProceedings of the 19th ACM international conference on Multimedia
Date Published2011///
Conference LocationNew York, NY, USA
ISBN Number978-1-4503-0616-4
Keywordselectric network frequency, information forensics, timestamp, video authentication

Electric Network Frequency (ENF) fluctuates slightly over time from its nominal value of 50 Hz/60 Hz. The fluctuations in the ENF remain consistent across the entire power grid even when measured at physically distant locations. The near-invisible flickering of fluorescent lights connected to the power mains reflect these fluctuations present in the ENF. In this paper, mechanisms using optical sensors and video cameras to record and validate the presence of the ENF fluctuations in fluorescent lighting are presented. Signal processing techniques are applied to demonstrate a high correlation between the fluctuations in the ENF signal captured from fluorescent lighting and the ENF signal captured directly from power mains supply. The proposed technique is then used to demonstrate the presence of the ENF signal in video recordings taken in various geographical areas. Experimental results show that the ENF signal can be used as a natural timestamp for optical sensor recordings and video surveillance recordings from indoor environments under fluorescent lighting. Application of the ENF signal analysis to tampering detection of surveillance video recordings is also demonstrated.