One of the questions most frequently asked of authors has one of the least satisfying answers: "How did you decide on the cover?
Because the answer to that particular question, at least in my case and the case of most authors with whom I've discussed it, is usually, "I didn't. I had nothing to do with it.
"
Authorial involvement with book-cover design usually boils down to this email you get, out of nowhere one day, as you're in the panicky final stages of finishing the book, and you've reached that terrible point where you are certain the whole thing was a terrible mistake, and you don't want to be a writer anymore and you'd like to go home now, and then along comes this email from your editor...