Johnson Space Center's Digital Image Collection

NASA's Johnson Space Center in Houston has put up 9,000+ photos from their archive online here. The database is searchable, and one page has several drop-down menus where you can browse several categories of photos. According to the site's FAQ, the photos themselves are all in JPEG, 640x480 and 72 DPI, so not a very sustainable format, but the FAQ also links to a site containing some (though not all) of the photos in uncompressed HD format. The site also says that the JSC is fine with the photos being reproduced under some pretty rigorous guidelines (see them here).

Each photo has a page where you can see a 640x480 version of it--again, not very clear--and a page where you can see a thumbnail of it and the metadata. (I'm not sure why they wouldn't merge the two somehow, but oh well.) The metadata itself isn't great--an ID number, what kind of film was used, date taken, the mission it's associated with, a title, a brief description, and subject terms. The subject terms seem to have been created by NASA staff. There's no mention of the photographer, or the creator of the digital object, either.

The site's creators seem to believe that people might want to reproduce these in certain publications, like magazines or textbooks or classroom materials, but they're probably not targeting scholars, like people interested in the history of the space program. If they were, I think they'd have a much better photo format and more robust metadata.