If you know someone that is cheating but don't know how to prove it

I wouldn't worry about pictures or anything like that , I would go to my friend and tell her what I knew and give her the option to believe me or not . My friends should know me well enough to know that I would never ever make up something like this and would never want to hurt them . I would definitely not ignore it as I know how it feels to be the last person to know and to be the one that was hurt . I don't believe in cheating on someone , if you no longer want to be with someone then you should have the guts to tell them after all they have the guts to go behind your back and do something wrong so they should have the guts to tell you to your face . When you tell your friend just be prepared for her initial anger , this does not mean she is angry at you it is just that she will need someone to strike out as she will be very upset and you will be the one in her line of fire as you are the one who told her but once she gets over her shock she will be grateful to you for doing something no one else had the guts to tell .