A work of authorship is in the “public domain” if it is no longer under copyright protection or was never entitled to copyright protection. Works in the public domain can be used freely and reproduced in any manner by anyone without the need for permission. Previously copyrighted material will fall into the public domain when the copyright has expired or the copyright owner has failed to comply with copyright renewal procedures.
The “Date and Country of First Publication” column of the inventory form will help you determine whether the material you will use has entered the public domain. The Public Domain Chart developed by Cornell University may be used to determine whether the copyright term of a work has expired and if, as a consequence, the work has fallen into the public domain.
If the item of third-party content has not fallen into the public domain, you should continue to assume it will require rights clearance.