If you don't have this at the end of the game.
Once you become the Big Daddy you'll have to protect little sisters. Take three photos let her get knocked out and get a new one, rinse and repeat until you unlock it.
IMPORTANT NOTE
If you do this save BEFORE you get the first little sisterand go back if you're going for Little Sister Saviour as for some reason on this version of the game this technique buggers it up.