Father Pitt has decided to release all his pictures into the public domain with a CC0 public-domain dedication. That means you can use them for any purpose without asking permission, but you can’t hold poor old Pa Pitt responsible for the results. It’s nice to credit “Father Pitt,” but it’s not required.
If you click or tap on any of the pictures, you’ll get the picture at its highest possible resolution—big enough to print as a full page in a magazine.