Measuring how well police surveillance cameras prevent crime is a tricky process since you're dealing with a vague set of variables. You can't be entirely sure if someone planning to commit a crime decided against it because of a police camera. Additional factors, such as the season, economy or other law enforcement tactics can also have influence.
For example, a study of different CCTV effectiveness evaluations from various jurisdictions in Europe and North America by the Home Office Research Group in the United Kingdom eliminated 24 evaluations from its research pool because of faulty methods [source: Welsh and Farrington]. Of the remaining 22 that the Home Office examined, success rates bounced all over the place, depending on the setting [source: Welsh and Farrington]. You can see how the reports on the subject range broadly.
Law enforcement officials are usually the most positive about the crime cameras. Some of the recent statistics provided by U.S. police departments claim the following drops in crime rates:
On the flip side, of the 73 cameras installed in Washington, D.C. since 2006, none have provided footage that has helped solve any crimes [source: Washington Post]. Also, the New York Police Department reported a 30 percent drop in crime in a tough neighborhood in the Bronx after camera installation [source: Lee]. However, the camera installations coincided with increased police patrols.
So taken as a whole, what do all these numbers mean? The Home Office Research Group conducted another more comprehensive study in 2005, confirming that CCTV networks appear nearly ineffective [source: Gill]. A similar evaluation from 2006 by the U.S. Department of Justice, also questioned the reported success of CCTV systems, finding little evidence that they significantly reduce crime [source: Ratcliffe].
This isn't to say that crime cameras are entirely useless. Evidence consistently points out that cameras reduce auto-related crimes as much as 41 percent [source: Welsh and Farrington]. They are also more helpful with reducing crime in enclosed areas with less foot traffic when combined with other law enforcement efforts. And they're helpful in conducting post-crime investigations [source: Ratcliffe].
Nevertheless, the 2005 Home Office study revealed that the cameras did not produce enough bang for the buck. Federal and state governments have poured millions into the set-up and upkeep of crime cameras, but the Home Office study revealed that they were underutilized and not fully integrated into police strategies [source: Gill].
This goes against the presumption that this kind of preventative measure would save governments money. To make cameras worthwhile, police must manage and use their CCTV networks more proactively, rather than handling them as self-contained tools [source: Gill].
In the mean time, as police surveillance cameras become increasingly widespread, one particular public relations problem lingers -- privacy.