This achievement is earned for finding optional photo #1. If missed on the first run, you can "Play Episodes" and select specific parts of the Episode in order to find the missing optional photos through collectibles mode. The following collectible is described and can be seen below:
] - Optional Photo #10
In the nightmare stealth section you'll end up at the junkyard and you'll need to collect all 5 bottle scattered around this small area. After collecting them, go to the next area and find the bottles on the desk. Take a photo of them and they will break, getting the last photo!
Collecting all 10 photos will also reward you with the following achievement: