There are two secret gamer pics that you can unlock. For the first one, you have
to complete any of the levels on Nightmare difficulty, and it will unlock a Demon
gamer pic. The other gets you a Doom Marine pic, and you get it by getting a 100%
kill rating on any level with a "Hurt Me Plenty" difficulty or higher.
CLEAN SLATE (5) : Kill all monsters in level on 'Hurt Me Plenty' or higher.
DESTROYER (10) : Get 100 kills on Xbox Live.
EPISODE FOUR (25) : Complete Episode 4 on 'Hurt Me Plenty' or higher.
EPISODE ONE (25) : Complete Episode 1 on 'Hurt Me Plenty' or higher.
EPISODE THREE (25) : Complete Episode 3 on 'Hurt Me Plenty' or higher.
EPISODE TWO (25) : Complete Episode 2 on 'Hurt Me Plenty' or higher.
HOARDER (5) : Find all items in level.
NEOPHYTE (20) : Complete any level.
NIGHTMARE (10) : Win a Nightmare level in single player.
RAMPAGE (35) : Complete all levels on UltraViolent mode.
ROOKIE (10) : Get 50 kills on Xbox Live.
SCOUT (5) : Find a secret area of a map.