Back in 2005, The Register reported on a UK police project (the article calls it Gatso 2) whose thrust was to use cameras to identify vehicles' license plates as they go by. The information on who/when/where (WWW) would be stored for at least two years, and the system was expected to process 50 million plates per day. They were planning to deploy the cameras on motorways at 400-yard intervals as well as in parking lots and other areas. Stated intent: spotting stolen cars and cars whose owners hadn't paid their insurance. (I'm having trouble learning how the project turned out, but I'm going to run with it as far as I know it.)
This all makes sense except for the part about saving the data for two years. Police can spot delinquent plates and dispatch squad cars accordingly without having to save the WWW data. And they can do something else: If they know the distance between the cameras, they can automatically calculate how fast your car is going. From a revenue perspective, automatic detection of speeding is very attractive: If you're caught speeding and you don't know it, you'll keep right on speeding. Which means you could be caught and fined repeatedly as you zoom along in happy ignorance. (And you won't have any idea how large your fine has become until they appear at your doorstep to extract a kidney.) But, even for that, they don't actually have to save the data.
No, the only reason to save the data is to facilitate backtracking. Backtracking is helpful if you have a suspect and want to know what he's been up to--where he's been and who's been there with him. This makes sense and should give the innocent (who, as always, have nothing to fear) a warm, fuzzy feeling of safety.
A cold, prickly feeling, however, should accompany this possibility: What if the data is hacked? Should that happen, interesting possibilities arise: Knowing which cars are in airport long-term parking, for example, would tell you who wasn't home--a quick look at their owners' credit reports would tell you which houses were worth "visiting." A little judicious data mining might even reveal blackmail opportunities: two married people (not to each other) showing up at the same hotels, for example, might let you write a pair of very remunerative letters.
But, those minor considerations aside, Gatso 2 is an innovative and exciting prospect that we should all welcome. Next time I'm in London, I'll give a friendly wave to its ubiquitous, reassuring, glassy-eyed Cyclopses...as I descend the stairs to the Tube.