This achievement is earned for finding optional photo #4. 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 #4
Outside the dorms, talk to Samuel, the custodian, and ask him about animals, then the squirrels which will make him feed a squirrel. Next interact with the food next to him to lure the other squirrel. Once they are together on the grass, snap a photo.
Collecting all 10 photos will also reward you with the following achievement: