It’s not always that clear cut. When these cases go to court, the rulings vary. One judge may deem it fair use while another may not. I never use images I’m sure are under copyright, but you can’t always be sure. My policy is when in doubt, don’t, but some people have won in court. (Of course, plenty others have lost, and who wants to go to court?)

This is an excellent article on the subject. https://www.format.com/magazine/resources/art/avoid-copyright-infringement-photos