The primary purpose of the cover is to identify the ebook, on Amazon Kindle, that it is in the Thriller/Mystery Genre. This is to help readers by telling them they've found another ebook in the area they prefer reading. This basic 'statement' of the design, that overwhelming identifies the ebook as a thriller novel MUST BE OBSERVED. With that said, having an appealing design with all parts working together is the next priority. My image attached to this design brief is by no means the only possible design possible. I can be convinced something else is a better book design, it need not be what I suggest next. If you need inspiration for a visual scene with impact I suggest the opening chapter. It has a strong scene in which a border station in the West Texas desert is attacked at night and explodes in huge fireball. The attacker looks on, in a prone position, serenely surveying the damage with the scope on his Druganov sniper rifle, enjoying it's beauty as people burn to death. The Border station or the people in it that are 'blown up' are not wanted in the image, as this may not match the description on the book. Better to show the fireball and a general fiery area and it's contrast with the dark sky above. In this image the fireball and the sniper rifle are most important, as is the desert decor', visible as shapes littering the foreground, main colors are black of night, red, orange and yellow in the fireball and traces of sandy beige, the desert where it happens to be marginally lit. The overall image and cover (in this concept) is dominated by pure black, evil outlines, the sniper and his rifle, with the tiny reflection of the sniper's optics. The image should make us wonder who the sniper is, what he looks like.