Oh, I wasn't even thinking about the photographer knowing. I've always told them as soon as we've made contact (before arranging to meet) that I'll be using the photos to advertise escort services and that I'll give whatever credit they want or leave their name off completely if they prefer. Not telling them just doesn't seem right in a TFP situation.
For those that are unfamiliar, TFP stands for Time For Prints (although these days you usually just get a CD of photos rather than prints), and it's a way that models and photographers can expand their portfolios without spending much money. You both offer your time and you both get pictures out of it which you can use to promote yourself. The important point here is that the photographer will expect to use some of the images with the same freedom as you have and he's probably going to have some pictures that are identifying. You can negotiate so that only headless pictures are allowed or something, but if you're trying to protect your identity I think it's just quite risky.