The artist, Kristoffer “Razorback” Frisk, emailed me back and said I had his blessings to use his work, “Fallen Angel”, on my book cover (so long as it wasn’t a commercial venture, and wished me luck.  Check out his portfolio on his webpage http://clik.to/razorback (the website menu is chained to the angel/demon pic).

 

Below are a couple of images of his I really liked: