Like it or not, it is a trust issue. You said so yourself. It's not really the idea of the
photographs being taken, as much as it is the idea that you can't trust that they'll be safeguarded the way you want them to be.
Here are my thoughts as a man on this topic. If he wants to take nude pictures of you, what's the harm in it? There is no shortage of pornography available, so it's a
compliment that he wants to have pictures of you. It could be a very intimate form of sexual play and bonding. Couples need to keep passion alive, and interest in their partners vibrant. I think it's a good thing that he's very interested in you sexually and you should encourage and indulge that interest, even if it pushes your own boundaries a little bit.
However, some cautions:
1. Do not use film. You'll have to get it developed and then you won't be able to control who sees them. Digital pics only!
2. Only do it if you trust (there's that word again) that your wishes regarding the photos will be respected, not just now, but in the future, even if things go sour in
your relationship. Have clearly established rules: 1. They never get posted online or emailed to anyone. 2. Decide how and where they are to be stored. 3. They never get shown to friends, or whatever else you agree on.
3. If you are really, truly uncomfortable with it, and you have decided not to do it, that is your right. Calmly and firmly say no, without making him feel guilty or "dirty" for wanting it. If he loves you, he should respect that. It would not be fair for him to keep asking, or pressuring you once you have given him an answer. It is
fair for him to check in, though, every once in a while, to see if you still feel the same.
4. It is still, most definitely, all about trust, whether, it's about what happens to the photos afterward, or trust of him personally, in order to be completely open and intimate while having the pics taken. Think about it this way: Would you still be reluctant to do it if you knew that you could control, with absolute certainty, who, if any, could ever see the photos?
I would suggest exploring that issue in more depth.
Best of luck.