The website (https://unsplash.com/) provides writers and other content creators with copyright free images to use on their posts.
You can search and find images to match your content.
You don’t have to give credit to the photographers, but I’ll advice you always do. Since they put these pictures for free use, the least we can do is give them credit so others can discover and use their work.
I hope this helps! If you have any questions, don’t hesitate to ask here or on Twitter.