Library of Congress
The Library of Congress is the nation’s oldest federal cultural institution and serves as the research arm of Congress. It is also the largest library in the world, with millions of books, recordings, photographs, maps and manuscripts in its collections.
The library maintains digital collections that can be accessed online. Here you can view, and in most cases download, photographs, drawings and documents about lighthouses.
They also have a service where if you have a research question or need help using the Library, you can get expert assistance from librarians & research subject specialists. It is called “Ask the Librarian.” Don’t expect a quick answer or technical assistance about lighthouses, but it is great when you have a general question or are trying to see if they have a particular book you are seeking. Go to: http://www.loc.gov/rr/askalib/y
The Library of Congress also houses the HABS/HAER/HALS collections which document historic buildings, structures, and landscapes with detailed drawings and photos. Many lighthouses have been documented in this collection. These downloadable records are in the public domain except for any noted restrictions on photos.
To search for digital photos of lighthouses in the entire Library of Congress catalog goto: http://www.loc.gov/search/?q=lighthouse