Under "The Commons," cultural institutions that have reasonably concluded that a photograph is free of copyright restrictions are invited to share such photograph under their new usage guideline called "no known copyright restrictions."

Photographs can be difficult to analyze under copyright law, not only because laws around the world differ with respect to scope and duration of protection, but because the photographs themselves often lack credit lines, dates and other identifying information. Libraries, museums and other cultural institutions have a great deal of experience with photographs because they frequently collect, preserve, document and study them in accordance with their nonprofit missions.

This page lists the Participating Institutions on Flickr. These sources will provide a massive collections of images.