Use Firefly and make the ground prop (the plane, not the construct) a 'shadow catcher'. There is a wacro for this. This will then arrange the shadow. Superfly does not have this facility.

If you put the street image on a square behind the figure, you will want to see the image and not the shadow because you have the shadow catcher for that. To avoid the picture being lit by the scene lights etc, make sure the image node is plugged into the ambient channel and not in the diffuse channel. Of course set ambient_value at 1.0 (or at least not zero) and make diffuse and specular values 0.0.