At SMF they have a pickup truck with cameras mounted that cruises the aisles. I've seen it mid-day in the long term lot.

Not sure why they're recording plates, but I'd guess it was to keep track of cars that may have been parked (read: abandoned) for long periods of time.

At SFO they check your plate as you exit the hourly parking -- I had the attendant ask me to pull forward or back up because his camera couldn't pick my plate up (presumably when you enter it's taken, OCR'd into a database, and automated to confirm the ticket).