@Georgia366,
If your husband was "asking for a picture of her face" then chances are he never met the person in real life and is just flirting with the person.
If your so afraid then you might as well research on child-monitoring apps for your phones that sends a screen-shot or copy of what they are using their phone for, or even an app that will record a phones activity via video or audio file you could pick up later.
Again that is his privacy and so far, he has not slept with this person. "Asking for their face".
I know tons of party-girls who are wanna-Be's and still associating with guys for fun because it is their fun. Texting, etc, etc, etc, is like playing jeopardy, gambling, or video-games for tons of people even those who are super-wealthy or proverty stricken
Let him have his fun. As long as he is not having xxx relations with them.