Unsplash is a great website. It's a free and open library with a ton of beautiful pictures. You can use them however you wish and you don't need to add attribution, though I'm sure your readers will think more highly of you if you do.
It's so great that it's the go to source of graphics for a lot of bloggers. The same images are reused over and over again.
I feel like this guy keeps following me everywhere:
I used that very same picture for my own article not long ago. Then I saw someone else using it as well. And then I saw it again. And again...
Unsplash is well aware of the high volume of reuse and in December 2019 they decided to capitalize on it.
Don't want your article to be part of a clone army? Then at least check your image with Google's Reverse Image Search before publishing.