Complete the following achievements to unlock Xbox Live Gamerscore points.

Alien Maggots are Gonna Pay (10 GP) Finish the "Hollywood Holocaust" level in under 3 minutes.
Come Get Some (25 GP) Complete "Shrapnel City" on any difficulty or in co-op.
Duke's Mighty Foot (10 GP) Step on 40 enemies after using the Shrinker on them.
Game Over (25 GP) Complete "The Birth" on any difficulty or in co-op.
Gonna Rip Em' a New One (10 GP) Get 100 total kills in ranked Dukematch games (Online).
Hail to the King, Baby (25 GP) Earn respect and get 500 total kills in ranked Dukematch games (Online).
Let's Rock (25 GP) Complete "Lunar Apocalypse" on any difficulty or in co-op.
Looks Like Cleanup on Aisle 4 (10 GP) Step in a pile of excrement.
Oomph, Uugh, Where is it? (10 GP) Find 70 secret areas.
Piece of Cake (25 GP) Complete "L.A. Meltdown" on any difficulty or in co-op.
See You in Hell (15 GP) Get 250 total kills in ranked Dukematch games (Online).
Shake It Baby (10 GP) Tip an exotic dancer.

Collect the indicated amount of Xbox Live Gamerscore points to unlock the corresponding art.

Unlockables

Alternative Pig Cop concept art 1 70 points
Alternative Pig Cop concept art 2 70 points
Bad Cop concept art 0 points
Duke Nukem Forever screenshot 1 200 points
Duke Nukem Forever screenshot 2 200 points
Duke's Vehicle concept art 90 points
Jetpack concept art 50 points
Octabrain concept art 2 30 points
Octabran concept art 1 30 points
Pig Cop concept art 10 points
Sonic Resonator concept art 50 points
Trooper Recon Car concept art 90 points