Until fairly recently, authors and artists had to comply with certain "formalities" required under United States copyright law, or risk an abbreviated copyright term. For example, under most circumstances, publishing work in the United States without a copyright notice would have resulted in the work immediately falling into the public domain. Moreover, a work published prior to 1964 had to have its copyright "renewed" during a one-year window 28 years after the first publication.

Critically, a timely copyright renewal application had to be filed by the artist or his estate, not by the publisher of the book in which his artwork appeared. Few artists complied with this formality. As a consequence, many artworks published prior to 1964 fell into the public domain in the United States 28 years after they were first published. The concept of a "renewal" copyright term was eliminated in the Copyright Act of 1976, but only for works published after 1977.

1. Grant Wood, American Gothic, 1930. From: The Art Institute of Chicago, Catalogue of the Forty-Third Annual Exhibition of American Paintings and Sculpture. Chicago: 1930.
2. United States Copyright Office, Copyright Catalog. http://www.copyright.gov.
3. Rockwell Kent, Mount Equinox, Winter, 1921. From: Rockwell Kent, Rockwellkentiana. New York: Harcourt Brace and Co., 1933.
4. United States Copyright Office, Catalog of Copyright Entries. July-Dec. 1960.