Successfully complete the indicated task in the corresponding game to unlock the art gallery for that title:

1941: Defeat the Krote, the level 4 Boss
Avengers: Successfully complete level 4 and rescue the girl
Bionic Commando: Get over 25,000 points
Black Tiger: Defeat the level 3 Boss
Block Block: Successfully complete an extended bonus
Captain Commando: Defeat Dr. T.W., the level 5 Boss
Final Fight: Pick up Eddie E's Bubble Gum
Forgotten Worlds: Successfully complete three stages
Last Duel: Get over 100,000 points
Legendary Wings: Find a "Lucky!" hidden area
Magic Sword: Reach level 20 of the tower
Mega Twins: Enter the Monster Castle
Quiz & Dragons: Get over 200,000 points
Section Z: Successfully complete Section E
Side Arms: Defeat the level 3 Boss
Street Fighter: Reach Thailand
Strider: Defeat Captain Beard Jr. in level 3
The Speed Rumbler: Successfully complete level 3 (Stone Hill)
Three Wonders: Finish one the games
Varth: Defeat the Steel Golem in level 15.