What's the trick to making wallpapers?

I'm a long time photographer and have several shots I'd like to turn into wallpapers.  I've resized them to the dimensions of the screen (400 x 800?) but when I try to to set them as wallpapers the image handlers always want to crop them to something square and small then stretch the image to the screen dimensions.  Definitely counterintuitive.  Is there a step by step guide somewhere that I've overlooked?

"The technology of a sufficiently advanced civilization will be virtually indistinguishable from magic."

Sir Arthur C. Clarke

I'm running Ascension/Absolution v.1.0 beta 8; an ICS ROM.  No Sense although I downloaded the Smartbeat Supremacy ICS port w/Sense 3.6 but haven't flashed it yet.  I'm very curious though.

My question was about the dimensions.  I now see what I overlooked in my logic/question.  960 x 800 makes sense because I realized that it is scrolling the background image as you scroll from home screen to home screen.