Well, there are various ways to circumvent this, but the most fun for noob photoshop users like myself is to make a cover of your own.
My friend Suri and I are super fans of Nalini Singh's Psy-Changeling series... and one day we were talking about models we thought would represent the characters best, but it's so difficult to agree on one! I had decided to have a go at making alternate book covers for the books, but alas! I ended up liking the covers that didn't have model faces that I decided to post them, what do you think?
The obvious main reason: if it's anything else but people depicted, then you're free to imagine the characters as you wish.
Here's the first book: Slave to Sensation!