I recall listening to a presentation on aerial photography by an operator out of Moorabbin. From memory, they used a larger twin engined a/c with the camera mounted on some sort of rail system and shot through the floor. When it was time to take the shot the camera quickly but very briefly moved forward on some sort of sliding system in an attempt to compensate the forward speed of the a/c. Allowed for some very clear shots as I recall.
But that is a long way from hanging out the door of a 172.