The backup camera is entirely analogue, zero computer required. All manufacturers use the same couple of camera modules which output standard composite video, which is why even nice cars have obvious analogue artifacts and distortions.

Even OEM headunits usually just consume a standard composite video input and switch to it when it has a signal.

This information is valid up until at least 2020, but it might be changing as cars get more advanced cameras and stupid-er head units. I bet Tesla just uses their existing cameras.

>not beeping if seatbelt not fastened

Also trivial to do with analogue electronics, which we have done for decades.

speed limit warnings are a dead end though. Impossible to do without some sort of technology to know what the "current" speed limit is.