Find a website that offers royalty-free stock photography.
Use the search feature to search for specific images for your book cover, or browse the pictures to get ideas and inspiration.
Review the licensing agreements or terms of use associated with using the photos. Some photos can only be used a certain number of times, or used only for certain media such as print or electronic.
Purchase a license that allows unlimited use of the photo on your book cover, website, blog and promotional materials. This is typically called an extended license and is more expensive than a regular license.