Help do I say anything

I went snooping on my partners tablet and found a picture from a girl in June of her topless it’s in an old WhatsApp folder on there, he deleted the app as one of the kids got on it and sent messages out... there’s no pics of him half naked or anything... and no signs anywhere else he would be cheating I have his passwords for everything his phone tablet and accounts... I was wrong for snooping but he has old pics of his kids before we knew each other and I wanted to get some for my step sons birthday this weekend... my question is should I say anything to him or let it go I really don’t think he would of been cheating but i want to know why she would of been messaging him pics like that... help???? Please ???