The cover image you choose needs to help create a look that has a beauty and balance to it. Something that brings the viewers’ senses more into the book by creating an attachment to the emotion exposed.
When deciding on a cover image, look to the metaphor, to the possibility of the viewer ‘filling in the spaces’… being too literal in your image may not be the best motivator!
We all live with different references to images. Finding and using ones that best suit your book subject, your purpose, and excite your audience’s emotions, help with the mental/emotional/logical buying process they go through to finally purchase, read, learn AND then want more… from you.