I think that's a cool idea. But I think the answer is as simple as it would require mounting a camera on the underside of the car. If you are going that route w

I think that's a cool idea. But I think the answer is as simple as it would require mounting a camera on the underside of the car. If you are going that route why not just point a camera at the speedometer right? Or integrate into the can-bus of the car and read it right from the onboard computer. I think the presented idea was probably something that was constrained by what you could do on a phone without interfacing externally.