One day I will write an article about the whole topic, but here a quick tip:
Just ask the photographer!
For example, I have a website about a certain animal and came across a scientist that is not only a world authority on the subject, but also an outstanding photographer. All his images are copyrighted and stated 'no use without permission'. So I asked for it, and guess what? He granted it for free! Not only that, he is also now my 'go to / may I pick your brain' guy when it comes to this subject ...
Never be afraid to ask, the worst you can hear is 'No!', the best is that you just made a great connection in your niche. And yes, the site in question runs ads / is commercial ...
SY
PS I know that this might be old news for experienced writers, but I thought it might be useful for less experienced ones ...