If you don't want to use "specially prepared pictures", then your best bet would be to use a single side square in poser.  Apply the background to it in the material room, and in the pose room resize the square to the dimensions of the picture.  Use the XYZ dials to move the square around and back, and use the scale dial to enlarge the square as needed.

"It is good to see ourselves as others see us. Try as we may, we are never
able to know ourselves fully as we are, especially the evil side of us.
This we can do only if we are not angry with our critics but will take in good
heart whatever they might have to say." - Ghandi