The Public Domain Mark 1.0 (PDM)

“No Known Copyright”

The Public Domain Mark is recommended for works that are free of known copyright around the world. These will typically be very old works.  It is not recommended for use with works that are in the public domain in some jurisdictions if they also known to be restricted by copyright in others.

A work may have limited or “hybrid” public domain status for several reasons.  Some jurisdictions have unusually long copyright terms, which may mean that a work free from copyright restrictions most everywhere in the world could still be protected by the copyright laws of that particular country.  Sometimes a work is no longer restricted by copyright in a jurisdiction because the author or owner failed to comply with local formalities such as renewal, where those formalities apply.  It could also be the case for works that are deemed not protected by copyright by operation of law in a particular jurisdiction, but that are afforded protection under the copyright laws of other jurisdictions.

CC does not recommend the Public Domain Mark for works with limited, hybrid public domain status at this time.