"No Known Copyright"

PDM
Our Public Domain Mark enables works that are no longer restricted by copyright to be marked as such in a standard and simple way, making them easily discoverable and available to others. Many cultural heritage institutions including museums, libraries and other curators are knowledgeable about the copyright status of paintings, books and manuscripts, photographs and other works in their collections, many of which are old and no longer under copyright.  The Public Domain Mark operates as a tag or a label, allowing institutions like those as well as others with such knowledge to communicate that a work is no longer restricted by copyright and can be freely used by others.  The mark can also be an important source of information, allowing others to verify a work’s copyright status and learn more about the work.