Compendium of U.S. Copyright Office Practices, § 313.2 (PDF), su copyright.gov, United States Copyright Office, 22 dicembre 2014, p. 22. URL consultato il 27 aprile 2015.
«To qualify as a work of 'authorship' a work must be created by a human being.... Works that do not satisfy this requirement are not copyrightable. The Office will not register works produced by nature, animals, or plants.»
The Compendium lists several examples of such ineligible works, including "a photograph taken by a monkey" and "a mural painted by an elephant".