If you have a wifi network you could use a foscam camera. I use it in the baby's room.
I have a wifi camera from Stem (iZon) that can be viewed via their iOS app. While it works pretty well for monitoring the house, it probably wouldn't do so well in a car - it requires an internet connection (not just a local wifi network) and there's a good 15-20 second delay from the camera to what is seen on the iPad's screen. So not very useful for a backup camera on a car.