My experience on trying to match up backgrounds is as follows. We have
done tests where the actual camera used for the photograph was located by a
surveyor. These co-ordinates were then used to try and imitate the view given
by the camera. Result…… a very slight change in camera angle can have
drastic effects in trying to match existing conditions.
Without going and figuring out vanishing points, viewpoint heights,
etc. you can end up with images that are reasonably convincing, but you may be
surprised as to how far you may be out once you have done the actual
calculations.
As with everything else in life…. nothing comes for free.
Enjoy
Jaan Lepp