DIE (Doom Image Editor) is a utility for
the seemingly endless tools for the DOOM
wad. (The game DOOM ain't gonna die out
for a looonnggg time.) You can Export an
Image from WADTOOLS (c) Jeff Miller
1994, and Import it to DIE.  Then you
can paint all over it, Import it back to
WADTOOLS, and Shazam.  Custom walls.