background art

[Iceman81]

hey guys, i was looking to do a sort of collage of characters, and i think im good in that regard, but how do you find an image big enough to create a background?  I was thinking of trying to do like a super smash brothers level sort of concept... Is there any way to do this easily? Like say start out with a ground level, and move up to the floating island and then into the space one.  I am unsure how i would transition the sky background part, or find images big enough to cover a 6' by 4' cab.