Just make sure that your background color is darker than the image, so that it recedes. If you are thinking of using a gradient, use a dark brown at the top, and fade that to black at the bottom, this will give you a nice sense of depth (and the people at the top are much closer to the viewer than the people at the bottom, this will enhance the forced perspective).
Whatever you do, mock it up in photoshop first to see if you like it!
--Joshua--