psdGraphics.com actually offers free backgrounds that are actually free - no sign-up, email or any of that. 5000 px wide. That'll do nicely.
I used some of the paper background images (parchment, old manuscripts) for some of the strange creatures that are online at Zazzle called Mythological Animals (not the Camouflage pattern, though).
LeviS Covert Camouflage Cargo Shorts LeviS Ripstop Camouflage Cargo Shorts