If you have internet access from your garage (WiFi) you could use a network camera like
this. A bt on the expensive side but does everything you want. It doesnt require a PC to be on and will email you or FTP images/video when it detects motion.
I bought two of these for my house and they work well. Do a search on eBay for network cameras and there are quite a lot out there but you the more you pay the better they are.