Life Is Strange

This achievement is earned for finding optional photo #5. 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:
[2:55] - Optional Photo #5
After breaking into the principal's office, take a picture of Chloe sitting in the office chair from in front of the desk.

Collecting all 10 photos will also reward you with the following achievement:

When you get into the principal's office, you will have to search for a key around the room, since there are no keys around you will be sent to find 4 different items to open the door.

The first one is a can of soda you can take from the pop machine.
Second item is sugar, located in the Chemistry room.
Third item is sodium chloride, located in top of a shelf next to the Skeleton in the back of the room.
Fourth item is tape, located in the Art room.

When you get all items, head back to the office to blow the door open, the alarm will go off, so head inside the office and rewind, you will be now inside being able to unlock the door from the other side.

After the cutscene is done, position yourself in front of the desk and take the photo of Chloe sitting on the principal's chair.

From the main menu select 'Play Episodes' and then 'Episode 3'.

Find and highlight 'High School - Evening' and then 'Play this chapter in collectible mode'.

Follow the video and press (X) to take the photo.