Toribash
Original Post
bumpmap textures changes the way light affects your textures. it makes them look more textured/realistic. but they only work on some versions of toribash.so thats why its worth more than regular ones.
BAD LUCK
im not entirely sure, but like firebolt said it affects the way light hits it, casting shadows and such. it might only work with shaders though i dont know

They don't appear to work for me in 3.86, and I've heard others saying the same. Would you mind posting a screenshot of a working bump mapped head?