How to find the original source for images used by Shorpy so you can edit and use them yourself legally. I also show a free editing tool to get stellar results quickly.

http://machinethinking.co/

Other image sites with Public Domain images or Creative Commons licenses:

https://pixabay.com/
https://www.pexels.com/

Currently waiting for my images which I'm releasing into the public domain to upload to archive.org.

Note: The items on the Library of Congress site typically say there are no known restrictions on use, ie out of copyright and freely available. It's still your responsibility to verify these claims as they are not assigning rights to you.