Surveillance is the monitoring of the behavior, activities, or other changing information, usually of people for the purpose of influencing, managing, directing, or protecting them. This can include observation from a distance by means of electronic equipment (such as CCTV cameras), or interception of electronically transmitted information (such as Internet traffic or phone calls); and it can include simple, relatively no- or low-technology methods such as human intelligence agents and postal interception. The word surveillance comes from a French phrase for “watching over” and is in contrast to more recent developments such as sousveillance.
Surveillance is used for intelligence gathering, the prevention of crime, the protection of a process, person, group or object, or for the investigation of crime. Surveillance can achieve this by three means: by deterrence, by observation and by reconstruction. Surveillance can deter by increasing the chance of being caught, and by revealing the modus operandi and accomplishes. This requires a minimal level of invasiveness. Surveillance can detect by giving human operatives accurate and live situational awareness, and / or through the use of automated processes, i.e. video analytics. Surveillance can help reconstruct an incident through the availability of footage for forensics experts, perhaps again helped by video analytics. Surveillance can also influence subjective security if surveillance resources are visible or if the consequences of surveillance can be felt. In order to determine whether surveillance technology is actually improving surveillance, the effectiveness of surveillance must be expressed in terms of these higher purposes.