From the free to use and reuse section of the Library of Congress website:
https://www.loc.gov/free-to-use/
Free to Use and Reuse Sets
This page features items from the Library’s digital collections that are free to use and reuse. The Library believes that this content is either in the public domain, has no known copyright, or has been cleared by the copyright owner for public use. Each set of content is based on a theme and is first featured on the Library’s home page.These sets are just a small sample of the Library’s digital collections that are free to use and reuse. The digital collections comprise millions of items including books, newspapers, manuscripts, prints and photos, maps, musical scores, films, sound recordings and more. Whenever possible, each collection has its own rights statement which should be consulted for guidance on use. Learn more about copyright and the Library’s collections.
Visit the millions of items in the rest of the digital collections:
https://www.loc.gov/collections/