Boyfriend asking for nudes.

So my boyfriend and I are long distance and I get that he wants to still somehow feel intimate with me when we can’t see each other but I hate it when he asks me like can you send a pic. Like to me it feels demanding in a way and I feel uncomfortable like what do I do now... idk. I’d rather just send a pic in my own time when I feel comfortable and happy to do so. I just don’t know how to tell him that without sounding weird.