There is a good discussion over at Schneier on Security about the value of London's surveillance cameras. It is useful to recognize the value proposition of detective measures - we don't expect to prevent malicious actions, we expect to increase the likelihood that the bad guys will get caught.
The value proposition of detective controls can be a bit trickier than it seems. From a Return on Security Investment (ROSI) perspective, the overall goal is to increase the costs associated with crimes and therefore:
- Reduce the number of incidents that occur through a deterrent effect;
- Increase the likelihood that bad guys will be identified;
- Contribute to the body of evidence available for a crime; and
- Shorten the time span of active investigation.
From a Return on Investment (ROI) perspective, the cameras may be much less expensive than alternative measures being considered (or replaced) for crime fighting.
Regardless of what side you are on, this is the right discussion to be having.