?  i'm not sure what you mean by "the prop part?"  if you mean the environment prop, you don't have to use it.  like i said, you can use a box with walls facing inward.  just put images on each side and the top.if you mean the shadow prop, i just wasn't sure if you were aware when you were suggesting people use the ground as a shadow catcher. a regular shadow catching ground doesn't take into account AO.  if you're going to give away or sell background images, it would probably be good to refer people to bagginsbill's shadow catcher.  but again, you don't have to.   do you mean his IBL generation prop?  because that's what i'm suggesting you use with your background images.  to generate images for your IBL.  but if the IBL generator is in a scene with a big empty space, where empty is the background color, the image won't come out right, and then your light won't come out right.