I see that the background images can stand on their own, they serve more like a backdrop than an interactive scene.  This is what I recommend:

Install a one-sided flat square plane from the Primitives Library.  It does not have to be hi-res.  In it's Properties panel, set your scale x and scale y to 2500 each (or whatever pixel resolution dimension the final image represents).  Turn off cast shadows. Enter the Material Room and connect an Image_node to the Poser Surface's Alt_Diffuse.  This should make your square image self illuminate and not receive shadows from other objects in the scene.  Make certain that the Diffuse_color and Specular_Color are set to white (255,255,255) and their values set to 1.  If you want to see the image in Preview, also connect the Image_node to Diffuse_color.  Go back to your Pose Room and now scale and move your square within the scene.

Here are a couple of scenes in which I use this technique:

http://www.renderosity.com/mod/gallery/index.php?image_id=1885493&user_id=343328&np&np

http://www.renderosity.com/mod/gallery/index.php?image_id=1884989&user_id=343328&np&np

Let us know if this is exactly what you would like to accomplish.