How does it work - rear camera

Been thinking about this for a while as it's something I'd like to have but don't at the moment.
How does the rear camera work? By that, I mean does the rear camera transmit over the CanBus system or is there a direct feed to the monitor? Or is there some other system?
I've seen a couple of aftermarket rear camera systems but putting in the camera would be untidy from what I can tell.
Many thanks,
David

the camera is mounted under the number plate recess and its part can-bus with a independent cable

I'm guessing the can-bus activates it but the independent cable is what takes the feed from the camera.
Hmm, will have to take a look where the camera would usually be.
Thanks for the pointer.
David