Taking photos of others in Public

What should happen when people take photos of others in public without their permission? I know of a few people this had happened to. One was my family members friend when they were out at the mall. They were walking then they caught a man taking a photo of my sisters friend while she wasn’t looking from behind. Another time this has happened to me a few years ago when I was about 15 years old, I was at the neighbors house and I was talking to his wife then from the corner of my eye I caught the husband taking a photo of me because I heard the camera flash sound then the wife started looking over at him and smirk a bit. After that I was scared to see them again. I went to school and I asked the teacher what I should do about it. She told me to not confront him. I also remember when I would come home from their house my dad would question where I was and be upset that I was there with them (I used to tell him I’m going on a walk around the block which was supposed to be quick then I would come back home about an hour later)