I've played around with 'backdrop' images when taking photos of minis before, and I came across a photo of an english country scene on Flickr. The colours looked like they would go perfectly with the scenery and grass mat of my miniatures table, so I sent the guy who took the photo an email, asking if I could use his image behind my figures when I take photos of them, and he gave me permission!
It's a great photo - blends in really well with my stuff! I cropped it so there's a thin strip of grass along the bottom, in front of a lake, to tie it in with the table's grass mat. Then there's a forest on the other side, and hills in the background.
Anyway, way better than a white plaster wall at the back of photos!