A few days back my classmate shared a picture of my mom (her facebook profile picture) on a subreddit for cum tributes, and sent a screenshot to me.

After much threatening and requesting I was able to get him to take the post down, but I am scared that he has shared her pictures and/or her personal information elsewhere as well, since she keeps getting calls from unknown numbers daily.

I am actually not sure what to do in this case. Both of us are underage (15 this year), so I am not sure if he can get into legal trouble if I report this. I don't want him to go to jail or anything,

I just want him to not do this in the future.

I am also unsure if I should let my mom know about this, because if I do then surely the situation will escalate much further, and it is also a bit embarrassing to discuss these things with her in the first place.

How can I have him understand that his behaviour was more than inappropriate and that he must not do this again?

Edit: Hey everyone. Thanks a lot for all the help that was provided in the answers! It helped me resolve this issue mostly. I let my mother know and she handled it from there by escalating to my friend's parents and even the principal of our school. He was expelled after a couple of weeks of discussion.

As for the questions on why I didn't want to involve cops on him, it's because he wasn't really a bully. He was actually one of the most helpful people I knew in my class, which is why I was so shocked to see him acting like this and hoped to settle this amicably, but he went a step too far.