WHEN?

It happens most times when you are in love with somebody and you trust him/her totaly. I know that you want to trust him/her and you can but, if you break up then he/she still have nudes of you. and they can show it to other people or post it on internet. And I think you don't want that. So even if your boy/girlfriend asks say no ALWAYS. 

HOW?

You take your clothes of, you make a piature and you send it to him/her. But again DON'T DO THIS! It changes peoples life's and not good.