Guy's Behavior

Why does my guy friend always take pictures of me (when I'm not looking)?

So.. I'm at uni and I've known this guy since last year. We got pretty close pretty quickly and I've noticed everytime we spend time together he always takes pictures of me (& I sometimes I don't even realise it!). We used to do everything together and we're in the same lectures, we do shopping, eating out, studying, trying out new activities (e. g. cooking/ice-skating/rock climbing etc). Soo.. we did spend a lot of time together. Later on in the year I realised he pretty much always takes pictures of me when we're together which I don't really like (& I've expressed this to him). When confronted he said its to make memories since he's going back to Hong Kong at the end of this year.. but it feels excessive and the fact he does it without me knowing/without my permission kind if bothers me. One time he told me his memory gets full quickly since he takes so many pictures.. and he was showing me pictures of his friends as well and gave me his phone for a bit. As I was going through it I found a weird/sexy picture of me.. we were eating at a restaurant together and I was bent down on the table.. & my cleavage was showing.. I got really shocked & I quickly scrolled it away but.. I've been really uncomfortable since. Even recently we were at an event and my friend noticed he was taking pictures and videos of me while I was doing henna on people for charity.. If she didn't see that I never would have known and he never would have told me either.. what do I do? Should I be concerned? Is this normal behaviour for guys?
Why does my guy friend always take pictures of me (when I'm not looking)?
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