Really no need for pictures
Now I can understand GreyMac that there might, without prior setup, have been created a grey (whats in a name?) area. From your (sarah555) posts it is indeed not 100% clear if you two have it absolutely clear this is a hard limit.
If you set "no (nude) pictures" clearly as a hard limit, then we are done discussing: No is no. Maybe have another talk with him if being unclear at the start might have caused this situation, but not give in. Maybe have another talk if this is just his/her way of trying to get what he/she wants anyway. But be ready to walk away and find someone better. You are worth it.
If you have not set this clearly as a hard limit, then there is nothing from stopping YOU to still set it as a hard limit and whatever his/her emotions about this is: If he/she is not willing to respect that, there will also never be trust.
A part of GreyMac posts might put you in doubt, so I simply have to reply to this:
I can tell you why he wants them, men are extremely visual creatures. We need to see it. It's hard for the male mind to visualize things and we like pictures . He wants them so he can think and fantasize about you when you're not around. AND, as a dominant, he wants you to give in on this point so he can have the confidence and control he had before you took it away from him by refusing to do something you had never mentioned was a hard limit.
This simply not true. We (men) do NOT NEED it. I am pretty sure most of us LIKE or WANT it (yes, including me), but we sure do NOT need it.
It might be hard for you to visualize things, but not impossible. With a little practice you get a long way. Sure, a pictures might help a lot, but at the end of the day you are still fantasizing.
Especially in this case: The master seems to have a lot of pictures of previous subs. Let him replace the face in his imagination together with all the other stuff he is changing / adding to the picture in his mind. No big deal. Maybe (yes, only MAYBE) you could consider giving him a picture of you in your swimsuit, so he/she has a face and some 'features' to build his/her fantasy on. But there is absolutely no need.
If a men / master needs a picture to be in control, then be honest about it that you are doing something wrong in the first place. You might as well ask the sub for his/her creditcard or housekeys if you need something materialised to
stay in control . As long as your country does not formaly re-introduces slavery and your sub becomes your slave, you will never ever be 100% in control, no mather what you do. Learn to live with that. Fix that last tiny bit in the setup you create with your sub (collar, chains, ritual, a ring, whatever), not with something that is outside hard limits.
Lets not give sarah555 any reason to doubt about. Yes, maybe sarah555 needs to have a good talk and make 100% clear what the hard limit is, but no, there is no need to allow the master to make pictures. Respect eachother and play on.