LawMeme links to a paper suggesting a cryptographic scheme to make traffic cameras that respect driver privacy:
The basic idea is to replace cameras that snap pictures of license plates with EZ-Pass style transponders. On detecting a violation, the traffic enforcement base station would demand that the violator’s transponder identify itself. The clever and well-known part of the scheme is that the transponder would reply not with its actual identity but with a pseudonym. Through some zero-knowledge proof trickery, drivers would need to come forward, identify themselves as being behind their pseudonyms, and pay their tickets in order to be able to keep their transponders working.
The clever and original part of the scheme is that the transponders would change pseudonyms rapidly — once a second. That way, the network of base stations couldn’t be used to track a single vehicle around, effectively keeping the network from being used for other kinds of surveillance. The truly neat part is that it’s possible to stitch together well-understood cryptographic primitives in such a way as to implement this rapid name-changing without weakening the condition that violators need to pay their fines in order to keep on driving.