I hope your publisher requested a "Model's Release" or Disclaimer from the woman you used on your cover. I hope YOU required her to sign permission to use her photo. Good friends, of course, would help you and volunteer for the photo. But nothing separates friends like money, especially when they see you making $$$ and all they got was a photo. Please be careful here.

I've designed two of my three covers. For River Bones, my thriller about to release, I purchased the right to use an architect's drawings of an 1896 Queen Anne Victorian. I saw the house on the Internet and based my story using that floor plan before deciding that I wanted the house on the cover. When I asked, they sent written permission. They asked for nothing in return. I promised them a credit in the front pages and a copy of the book.

I also set the book in my childhood hometown area. People there are now waiting with bated breath for the book's release.

In your case, please use caution even though it's after the fact. And good luck in your book sales. It really was a good idea to use a friend's picture. It incites instant interest in your book.