Getting an image suitable for Warhead wasn't too difficult-- I was actually able to find a US Army photo of a Nike missile being launched from the very Nike site that I chose for the plot of the book. Little doubt about its being appropriate for the subject matter. The only problem, the Army image was in black and white and the covers of my books were in color. I had the cover designer do the missile picture in a light sepia tone to give it a hint of color, and the result was quite satisfactory.
One of the critical scenes involved a shoot-out, one of the characters armed with a modern precision rifle, the other with an antique Sharps buffalo gun. Having an example of each, I photographed them for the back cover. So far, I was reasonably successful in keeping the covers in tune with the content.