Obviously, in gmax it's easy, pop the backdrop image into the opacity slot...

It appears that you can map a transparent cross section polygon - sort of.

on a whim I made a square texture - just a basic outline shape - a star - and set it to black background and applied it to a square polygon.  

IN the texture definition, I left the fallback color 255,255,255 and alpha=0



Polygon material properties are default, except for alpha=0



The result is a transparent background polygon, with a white outlined "cross section".  Okay, only visible in the 3D window, but we already know how to bend, fold, spindle and mutilate vertices just by looking at the preview window, right?




Hope this is useful!