I'm don't see how a front mounted camera could reliably differentiate between a high overpass farther away and a lower one nearer to the vehicle; it has (basically) no way of determining distance, just angular offset from the centerline of the camera. With a binocular camera system and a bunch of computer processing you could get around that.
Rear view backup cameras can estimate distances on the ground by assuming the ground is a flat plane underneath the vehicles wheels, so the distance is directly related to the position seen by the camera. That doesn't work overhead (nor does it work if the ground slope changes beyond the wheels--as an extreme example, if just in front of a vertical wall).
