A couple of weeks ago I gave a talk on the traditional vs. self-published experience for writers. I discussed covers, but had to stick to those with new art created by artists, since I had no experience with photo covers. If only I'd been quicker about reading the May/June 2014 SCBWI Bulletin, I would have had some good info I could have included.
In that issue, author Chris Eboch had a great article called Photo Cover Design for Self-Published Novels. She uses a case study of an author who found the main photo for her cover herself and still needed a photo artist and a designer (that's two different people, folks) to finish her cover. I mention this to make sure everyone understands how involved creating a cover is.
Finding this article will be worth the effort for anyone thinking about creating their own book cover.