Los Angeles parking enforcement has it. There is a car with cameras mounted all around it, and it takes pictures of every license plate. They identify people with past-due tickets, expired registration, and stolen vehicles.

Not even necessarily a smartphone. Set up a camera at your window hooked up to a spare machine, take photos when motion is detected and look for license plates.

You can probably automate the whole process.

I'm partly excited and partly worried about the implications of how easy automated data collection like this has become. Imagine doing the same with face recognition software or RFID drivers' licenses.

Privacy issues aside, it would be a fun dataset to play with.

I don't really know how to feel about it. On the one hand, it's an invasion of privacy; on the other hand, you can't really outlaw data collection in a public space, can you?

Anyway, tales like A Scanner Darkly seem oddly prophetic and relevant: http://ahprojects.com/c/itp/thesis