I just spent a frustrating hour searching for the image that I used on the Ghosts cover. I think I've basically decided that it is the real and final cover (maybe some tweaking), and so even though the image was public domain, I wanted to credit the photographer and the website on the copyright page. Argh. Of course, I bookmarked the site, but then I lost all my bookmarks.
For future and current reference: Lightning Strike by Adam Weeden is the original image.