If I license an image to a client that is actually incorporated into a published work, is the publication date the date it was published or the date I sent the image to the client?
Either date could constitute publication. Where a work is distributed to one publisher for further distribution in a book, there could be a reasonable argument that the work was published on the date that the copies of the book were distributed to the public by sale or other transfer of ownership, or by rental, lease, or lending. But for purposes of the statutory definition the Office also would accept the claim that the work was published on the date that the photographer sent a copy of the image to the publisher.
Rob Kasunic, Director of Registration Policy and Practices at the U.S. Copyright Office