I've been approached by publishers putting together photo books and wanting to include one of mine. I've felt comfortable with it because: 1. The request came from a reputable publishing house, 2. I would be given full credit for taking the photo, and 3. I would receive a complimentary copy of the book.

Heh! None of the above, rhapsodie. That's what I thought: Can I at least get comped a copy?
:-)

You have no obligation to say yes and very little to gain. I'd ask for money.

See if they're going to give you money. Say something like "This is a very personal photo, and I'm not sure how comfortable I feel about having it out there in the world. I didn't feel this way when I submitted it, but I do now, having had time to give it serious thought. So I'm not sure I'm willing to do this without some compensation."

They will probably say no, but if they say yes, awesome!

Assuming they say no, let them use your photo for giving you credit. Being credited in a photo in a print book -- pretty damn cool, and possibly useful in the future.

Hmmm, photo credit! Thanks, treepour, there's an idea! That and a comped copy of the book might make my day. I drive a hard bargain.
:-)