Merlin looks most heartbroken in the last one like he is just done. It's really sad because Arthur is the last person Merlin has in life and he dies and all Merlin can do is cry and think of all the times he and Arthur had
didn't he also have to get thin enough to slip through the bars?<<<< I'm assuming that he got thin extremely fast (considering the conditions of Azkaban) and that he didn't realize that transforming blocked his emotions after a few months.
The ray of light peeking through the crack creates a blinding effect on the subject. The light is so bright that it blinds her vision, covering her eyes in the photo. The black and white filter makes the ray of light even more bright.