My wife's boyfriend keeps sending me photos.

My (f28) wife and I (m30) are in a relationship where she sleeps with other men but her current boyfriend keeps sending me photos of her intimate parts immediately after sex.

I've asked him to stop and when he ignored me I asked my wife why he keeps doing it and she keeps saying he's just messing around.

I've asked him to meet me for a coffee tomorrow morning to talk about it and he's agreed.

How do I confront him in a way that will make him stop?