If you use an image of a dog, it must be a pit bull. If you use an image of a man, make him in his 50s, and very gruff, straggly hair, skinny, country.
This is the first book in a series. I'd like the format to remain consistent through each book, so the title and background image can be changed, but the format, font, and overall look can stay the same, providing continuity. See the example of the current cover. As soon as I pick a winner, I'll be ordering more covers for the series.
Story elements that could be used to create tension on the cover: the book is about a man seeking revenge on people who stole his dog and fought him in an illegal fight circle. He is a backwoods moonshiner. He talks to his dog and the dog talks back. I've found in advertising the book that an image of a still in the woods converts very well. The protagonist carries a smith & wesson revolver, and is quite scraggly and gruff. He eventually poisons twenty men with wood alcohol. Though I wouldn't want that specifically on the cover.