If the law is such that the owner is guilty regardless of who was driving, but the owner can opt to reassign the fine to the driver if they have the willingness and the evidence to do so, then proving innocence isn't really what's happening if the driver opts to do it.

That said, if merely being the owner of a tool is sufficient to be guilty of whatever infraction someone else performs with said tool, that has 2 problems beyond the whole "proving your innocence" debate:

1. Why stop climbing up the chain at the current owner when you could keep climbing and say it's all the fault of the manufacturer? I jest, but this illustrates why, despite my first paragraph, it's indeed only sensible that the driver be at fault, so the government must prove who was driving.

2. Why treat cars differently from, say, weapons?