This achievement is unlocked as part of the storyline, in the Fort Frolic section of the game. Simply kill and photograph all of the people Cohen asks you to and place their pictures in the display case on the stage.
WARNING: It is essential that you DO NOT kill Cohen when he appears at his masterpiece. Killing him renders other achievements such as Weapon Specialist unobtainable, as you need access to Cohen's apartment (found at Olympus Heights laterin the game) and the only way to get at them is for him to unlock his door from the inside, which he won't be able to do if he's dead.
I learned this the hardway and now must do another playthrough. So thought I would add a note to deter others from repeating my mistake.