My girlfriend's ex boyfriend has nude pictures and videos of her and is using them against her, she is 16 and he is 17.?

[Alex]

My girlfriend and I have been dating for awhile, everything was going great until her ex bf found out we are dating. Then she found out he kept the pictures and videos he sent her while they dated for 3 years. We got a friend to get him to admit that he has the pictures and he has even uploaded on of them on twitter but only shown waist down.

I am just trying to get this cleared up because it has been ruining our relationship and her ex has been saying he's going to put them on twitter and instagram and spread them through her school. I just want the pictures to be gone for good, She has learned her lesson and I told her don't even sent that kind of stuff to me.

I am hoping that their is something I can do or that she can do so this is all gone and won't effect her future.

If the only way to do this is legally Will she get in trouble and if so what would be the punishment she and him would receive.
I have the evidence of everything he's said about how he has the pictures and videos and how he put them up online and how he is going to spread them all over. I just want to know what can we do and what would be the repercussions to the solution

Anything will help thank you for your time.
If we take legal action and talk to the police what would be the consequences for her?