Been trying to have something on the other side of the window on interior shots. Trouble was many of the availabe exteriors were distorted by wide angle lense photos. So this is the workaround I stumbled on: Put the photo, less sky, on a curved surface, remove the sky (optional) and add day or night Poser sky. Photo is from Corbis of the Ginza in Tokyo at night

Looks pretty cool, I've also tried making concave forms to put background images onto.

Also working on a sphere with interesting results