Moderate spoiler warning!
You must first reach the part of the episode where you wake up in Chloe's house. After Max is dressed, Chloe will ask you to go downstairs and talk to Joyce.
The moment you leave Chloe's room, look to the right and you'll see the open bathroom door. Go in, look in the mirror next to the toilet and you will be prompted with the option to take a photo.
Do so and the achievement will unlock.
Reabo has me another video to use; special thanks to him!