Once you recieve the camera, just use it to take a picture on any enemy.
You can earn the achievement faster by playing the "Worlds of Hurt" challenge.
Kill the splicer in the first room, and get your "gift" off the Little Sister.
One thing that she gives you is a camera!
Either take a picture of the dead splicer's body or of the Big Daddy in the next room.
(I got it off of the Big Daddy)