Depends, if he sees nothing wrong then he might be pissed that you don't trust him. Girls do this too, if you ask them to stop talking to some guy coz you know he wants to bang her: she'll say it's not like that and she'll be pissed that you don't trust her.
You can't ask him to stop talking to anyone, that shows insecurity and mistrust which isn't healthy for any relationship but he should tell the girl to stop sending selfies. There is no reason for that. She is disrespecting the relationship by sending them and he is for condoning it.