Hi and welcome Louise.
I can't comment on Adultwork as I've never used the website. But as far as sending you a picture of himself and his daughter, it might actually show how genuine and unassuming he is, if not a little naive and thoughtless in sending a family photo. Men and women don't think the same when it comes to something as incongruous as that. They see nothing wrong with it, whilst (generally speaking) it's not really something a woman would do.
I've had bookings where a guy has sent pictures of himself and his wife/partner/girlfriend together either on holiday or at some social gathering. I've chastised them and said that it's an inappropriate thing to do, as they have no idea who I am. I could be a really nasty piece of work that does a bit of blackmailing on the side. This never occurs to them.
You say you've had a few exchanges with him, so he obviously felt comfy enough to send you such a picture. Maybe when you see him you can gently tell him that sending family photos isn't really the appropriate thing to do.