You can't judge a book by it's cover, but folks do. Every day.
A book cover should drive to the core of the book and show it's soul. That is what I do: I visualize the souls of books.
My process involves reading the manuscript and creating several sketches of different concepts for the cover. I work closely though out the process with the publisher and author to be sure that the cover is everything needed and desired. Book covers, like the books themselves, go through many revisions. I will be there, pleasant and willing through each revision. Whether it is changing all the fonts, tweaking the colors, or just moving the title up a 1/4", I am there to get it done and ready to be sent to the printers.
As I am a designer and artist, I can work with existing photographs or create a custom illustration. I can also meld the two together, as you can see in the Birding in the Face of Terror cover in my portfolio.
I look forward to reading your book and creating the image that will be it's visual voice!