That's the question I received in an e-mail the other day from a very concerned reader. She'd stumbled upon another author's book with the same cover image as mine. Not exactly the same, of course, but the male cover model was the same as the one on my book, "Omarati."
What a lot of readers don't know is that covers are made (most, not all - some publishers have in-house artists or use freelance artists who come up with their own drawings or digital renditions) with stock photos. Basically the cover artist and author collaborate on a vision for the cover, and then the cover artist goes to different websites in search of something that works. When they find an image they like, they buy it, along with a license to use it. So it's not impossible, or uncommon, to have two different covers of books written by two different authors, published by two different publishers that have the same or similar images. Why? Because there's only so many stock photos that work.
www.istockphoto.com is one site that's really cool. Lots of interesting images and even some videos.
So, no worries. Calliph hasn't been hijacked. :-)