Sounds very much like 'rules for thee and not for me', which in my oppinion is a big red flag.

I don't think there's actually anything you can do to make him stop this behaviour. Frankly, it sounds like he might be one of those people where if you try to enforce change, he'll just start hiding it yo get you off his back.

I think the biggest questions in this situation are these:

Why is this a problem for you in the first place?

Do you think he will go further then just jerking it to pictures?

Is this a deal breaker for you?