The public domain comprises the body of knowledge and innovation (especially creative works such as writing, art, music, and inventions) in relation to which no person or other legal entity can establish or maintain proprietary interests. This body of information and creativity is considered to be part of the common cultural and intellectual heritage of humanity, which in general anyone may use or exploit.
If an item is not in the public domain, this may be the result of a proprietary interest as represented by a copyright or patent. The extent to which members of the public may use or exploit an item in relation to which proprietary interests exist is generally limited. However, when copyright or other intellectual property restrictions expire, works will enter the public domain and may be used by anyone for any purpose.
No legal restriction on use
A creative work is said to be in the public domain if there are no laws which restrict its use by the public at large. There may be no laws which establish proprietary rights in relation to the work, or the work or its subject matter may be specifically excluded from existing laws.
The underlying idea which is expressed or manifested in the creation of a work generally cannot be the subject of intellectual property laws (see idea-expression divide). Mathematical formulas will therefore generally form part of the public domain, to the extent that their application in the form of software is not covered by copyright.
Works created before the application of intellectual property laws also form part of the public domain. The Bible and Qu'ran, the works of Homer and the inventions of Archimedes are in the public domain. However, intellectual property rights may subsist in translations or new formulations of these works.
Although intellectual property laws are not designed to prevent facts from entering the public domain, collections of facts organized or presented in a creative way, such as categorized lists, may be copyrighted. Collections of data with intuitive organization, such as alphabetized directories like telephone directories, are generally not copyrightable. In some countries copyright-like rights are granted for databases, even those containing mere facts. A sui generis database rights regime is in place in the European Union.
Works of the United States Government and various other governments are excluded from copyright law and may therefore be considered to be in the public domain.
Creative Commons [1], an organization which promotes the migration of works into the public domain, and copyleft licensing schemes, considers that:
"Public access to literature, art, music, and film is essential to preserving and building on our cultural heritage. Many of the most important works of American culture have drawn upon the creative potential of the public domain. Frank Capra's It's a Wonderful Life is a classic example of a film that did not enjoy popular success until it entered the public domain. Other icons such as Snow White, Pinocchio, Santa Claus and Uncle Sam grew out of public domain figures."
United States law
Generally, it is held under Feist that Congress does not have the power to re-copyright works that have fallen into the public domain. [Eldred v. Ashcroft transcript] But re-copyrighting has happened before. "After World War I and after World War II, there were special amendments to the Copyright Act to permit for a limited time and under certain conditions the recapture of works that might have fallen into the public domain, principally by aliens of countries with which we had been at war." (Testimony of Dorothy Schrader, general counsel of the U.S. copyright office, hearing for H.R. 1623, serial 100/50)
Works created by a United States government agency are public domain at the moment of creation. Examples are: NASA photographs, military journalism, federal court opinions (but not necessarily state court opinions), congressional committee reports, census data, etc. Availability of such documents may, however, be limited by secrecy laws.
Before 1978, unpublished works were not covered by the federal copyright act. This does not mean that the works were in the public domain; it means that they were covered under (perpetual) state copyright acts. Web sites that claim that "pre-1923 works are safe" are wrong for unpublished works. These works not published by 2002 are under federal copyright for life plus seventy years.
Until the Berne Convention Implementation Act of 1987, the copyright term in the United States was only five years for works published without a copyright notice, unless the work was registered with the Library of Congress in that time period.
Critics of copyright term extensions have said that Congress has achieved a perpetual copyright term "on the installment plan." Statement of Professor Peter Jaszi, The Copyright Term Extension Act of 1995: Hearing on S.483 Before the Senate Judiciary Comm., 104th Cong.
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