Just discovered Bing lets you disable the BG image on its front page and all subsequent results pages.

It's linked directly from the main page when you click the "Help" link: http://help.live.com/help.aspx?project=wl_searchv1&marke...

And you'll see there that the links to do the actual toggle are simply:

http://www.bing.com/?rb=0

and

http://www.bing.com/?rb=1