He will probably need a microPC or similar in car with a GSM card and CCTV card so it can both record images and send them over the mobile network to a pc.

Not difficult to do as there are plenty of CCTV software and systems out there that can do it. Also plenty of covert cameras suitable too.

The problem you will find is transferring the data live over the internet. Probably needs 4 cameras, and a decent resolution on each plus potentially sound. That will take a lot of bandwidth. would cost alot of money too unless you can get a proper unlimited contract sim to use in the unit.

If its for home use in the garage, then hed be better doing it over wireless.