PLEASE HELP!!!!

Okay so I'm in 10th grade in high school and there are these two boys that constantly take pictures of my butt. I have asked and told them to stop, but they havent. I feel VERY uncomfortable standing because I feel as though they are judging me and taking pictures of me. After they take pictures of my butt they post it on a group chat and the group chat is for the whole football team. So the whole football team has seen the pictures. A couple of guys have told me about it and thats how I know they are posting it to the football team group chat. What should I do? O don't want to be the snitch, but I'm pretty sure this is sexual harassment of something like that. PLEASE HELP!!!!!! And if I should tell an adult, who should I tell? The principal? A teacher? PLEASE HELP!!