It is not impossible; but you are talking about cutting edge object detection and interpretation. I've seen demos in tech blogs, but nothing like a real product.
I willing to guess that a developer could build a single scenario app fairly easy. It would require something like pointing the iPad 90 degrees to the path of the car and letting the car drive by.
Anything more complicated than that is going to require the iPad to 'understand' the video well enough to determine what angle you are viewing, what the landmarks are, how far away they are, and witch object is the car.
What's easy for humans is hard for computers, and vice-versa. Understanding a complicated scene is easy for humans. It's really really hard for computers.