Why is he secretly taking pictures of me?

There is this teacher who teaches at my school. He isn't my teacher yet I'm always seeing him all the time

- the other day I was working on a timed essay in class. I had my back turned to the door. Then I trned round and he was standing in the corridor with his phone help up and pointing my direction. When I saw him he quickly put his phone away and walked off
- another time he walked into one of my lessons. He talked to the teacher then sat down next to me and turned to face me with his iPad pointing in my direction. He stayed there for a good 10 minutes and then left
- one day I was in class standing up listening to the notices and he walked in and stood near to me and was staring at my face for ages. I then rolled my eyes and he laughed and then when I was walking out he followed me with his phone help up and pointing in my direction, then when I caught him he quickly walked off the other way
- sometimes when I'm in a room on my own he will burst in and stand there staring at me for ages and walk out without saying a word
- he always seems to be around me and stares at my face and body a lot. Sometimes he will stand in close proximity to me and stare at my face for a long time
- sometiems when I'm sitting down in class he will walk past me and his crotch area brushes against my shoulder even though there is space for him to walk. This has happened more than once

Why is he doing this? I feel like he is secretly taking pictures of me?

Read more: Why is he secretly taking pictures of me?