Attached Link: http://www.morphography.uk.vu/dlprop.html

I never use Poser's background image import, unless it's temporarily to hold a reference image for a portrait or something like that. Applying your image to a square prop gives you a lot more flexibility; you can also use a basic backdrop box like mine (download it at the link). At other times, I prefer to composite the background image in an external program. If you can't afford Photoshop or Paint Shop Pro, The Gimp is free and will do the job for you just as well.