Ok don't know if this will be useful at all, but I uploaded them, so thought I would pass the word along. But i often use backdrops in my renders, and have been going through a crap load of photography I have done in the past 5 years. so here ya go. Not sure if useful but i do hope that it can help both new and advanced users in rendering with backgrounds, hey maybe even useful for the cyclorama environment, never have tested it for that though, so maybe. anyways links provided below.

Atlantic Ocean Backgrounds

http://www.sharecg.com/v/45627/view/Poser/Backgrounds-Atlantic-Ocean

Meridian Hill In Washington D.C.

http://www.sharecg.com/v/45628/view/Poser/Backgrounds-Meridian-Hill

Nature 1 Backgrounds (Taken @ Soldiers Delight near Sykesville Maryland

http://www.sharecg.com/v/45629/view/Poser/Backgrounds-Nature-1