in some countries for some uses, such as for criticism or review, or for educational purposes, the law permits you to copy without having to ask for permission. So it depends where you live, and what you want the copy for. If your local law does not give you such permission to use, then you'll have to approach the author or publisher for written permission instead.
It really does depend on the country. If the author/photographer/creator copyrighted the image in the U.S., your use of it could be found to be liable for infringement. If they are U.S. photographers, it would be wise to contact the photographers (or whoever owns the copyright, if it was works for hire), and request a license to use the images. You may have to pay money for such a license, or the photographer may simply be satisfied with the publicity. Most savvy photographers use a copyright notice on their images, which makes it easier to locate the owner of the copyright. Here is a link that has more detailed information: https://9wdigital.com/the-correct-copyright-notice-on-a-photographers-website/
You just need to follow the link "Rights and permissions" or "Reprints and permission" which is being in the article page. It will direct you. It's a very simple way.