Re: This should be one of the easiest taxes to collect ...
Problem is with the "Car located" step. Serious dodgers have ways of getting hold of cars that have an incorrect keepers address or have been declared scrapped.
So unless they are stopped by the Police with the power to impound the car, then driving past a noddy DVLA ANPR vehicle is of little consequence to them.
Especially as the ones I see round my way with surprising (and I would imagine expensive) regularity all sit there with very visible flashing orange lights that can be seen way before a handy turn off.
With a paper disc, anyone walking past the car could see it was untaxed. That in itself had a deterrent effect.