Just to make a point: it's not a selfie if you take the photo of someone else!
Answering the original question: this situation has never come up for me, and I guess it would depend on context. However I find it hard to imagine a situation where I would be happy with the encounter being recorded. Two questions would come to mind: firstly, where are these photos going to be shared? I'd be very sceptical if the answer was "No they won't be shared, I'll just keep them to myself." Sure, sure, and I'll still respect you in the morning. Second: Is that why you're getting with me? For a photo shoot? Here was I thinking it was because you fancied me as a sex partner.
Unless it was someone I already knew well, I think I'd politely decline, and if he was insistent then I'd start getting dressed and say "Find yourself someone else to perform as a model, I just wanted to have sex."