I had the chance to review one of my covers early on with a VP from a Marketing/Advertising firm. A couple of the key points that stuck with me from that session I will share.
You want people to identify with your product (book in this case). She shared an example of a product her firm had rebranded (labeled). The largest difference from before/after was they had added a child's face to the product packaging. Sales went up 30%.
Faces (person) help people identify/connect with a product. In lieu of a visage, hands or someone wearing jewelry are also good items. In fantasy, amulets work for this. In sci-fi, gizmos.
I know there are tons of examples of really successful novels without a person/face on the cover. Don't bother posting them all for me

I spend hours in bookstores looking at covers in my genres and out--seeing what works and what doesn't. I don't spend much time in the paranormal area, so I would suggest you do that for yourself!
Finally, spend some money on a cover artist. I understand stock photos are free (relatively) but the cover is the best advertising dollars you will ever spend on your book. Judge an artist (as Lou Anders once shared with me) by the worst piece in their portfolio, not their best. Don't hesitate to go to Eastern Europe to find an artist, they work for slave wages; great talent in Poland and other areas. The cover art will sell the book.