Under the laws of the United States (and of European countries, through the Berne Convention, and of members of the World Trade Organization through the WTO Agreement on Trade-Related Aspects of Intellectual Property Rights), copyright is automatically attached to every novel expression of an idea, whether through text, sounds, or imagery. For example, the words in this paragraph are protected by copyright as soon as they are written. This also applies to diary entries, letters, song lyrics, and drawings, even if they are only done "off the cuff," in the most casual of circumstances.
For example, a drawing of a dog made on a café napkin is copyrighted simultaneously with its creation and is the sole property barring any contractual abrogation of the copyright of its creator. This drawing cannot be copied, displayed, or otherwise commercially exploited by any person other than the creator for the life of the copyright. Among other things, no person other than the creator has the right under copyright law to create "derivative works" works that depend upon or develop from the original, copyrighted work. This limitation is of particular significance to open source licensing, as will be explained later. In the United States, the period protected by copyright is very long indeed: the life of the creator plus 70 years, or in the case of works made "for hire" or by creators who are not identified, 95 years from the date of publication or 120 years from the date of creation, whichever is shorter.
This does not mean, of course, that the creator of this drawing has a monopoly on the depiction of dogs. Copyright law does not protect any particular idea. Rather, copyright protects only the expression of that idea. The creator of the dog drawing has a right to the commercial exploitation of only that particular expression of "dog." This right is no limitation on the right of others to create, and to commercially exploit, their own expressions of "dog," whether through drawing or other media. This limitation to expressions excludes protection from copyright of creations that are not expressed in a tangible, reproducible medium. For example, a dramatic monologue read on a street corner is not protected by copyright. However, if a reading of that monologue is recorded, whether on audio or videotape or paper, it is subject to copyright protection.
This limitation to the expressions of an idea is the principal distinction between the applications of patent and copyright. Unlike copyright, a valid patent does not protect the expression of an idea but the underlying substance of it. For example, a patent applicable to a microchip protects not the expression of the chip itself, or the electrical diagram describing it, but the idea that given circuits can be organized and made to operate in a particular way. Because of their potentially vast scope, patents are construed more strictly, require a registration process, and last for shorter periods than copyrights.
A copyright does not need to be registered to be legally effective. As already noted, a copyright comes into force when the protected work is created. While registration of the work with the United States Copyright Office has some effect on the rights of the copyright holder, it is not required. Moreover, while works published previous to March 1, 1989 need to bear explicit notice of copyright protection or risk losing that protection, works published after that date do not. Nonetheless, use of a copyright notice alerts potential infringers that the work falls under the protection of copyright.
The vesting of copyright protection in the creator of a work is subject to two important limitations: the doctrines of "work for hire" and "fair use." Works that are made "for hire" are made by an employee in the scope of his or her employment by another, including those that are specially commissioned for use in another work or as a supplement to another work, such as a translation. Works that are created "for hire" are still subject to copyright protection, under the same terms as described above, but the copyright belongs to the employer of the creator, or the person who commissioned the work, not the creator.
The doctrine of "fair use" defines certain uses of copyrighted material as non-infringing. "Fair use" allows persons other than the creator to make certain limited uses of the copyrighted material for purposes of commenting upon or criticizing the work, reporting, or teaching related to the copyrighted material. "Fair use" is a flexible standard, and whether a particular use is considered "fair" depends in substantial part on the extent to which that use impedes the copyright holder's exclusive rights to commercially exploit the work. In addition, one additional category of work is held to be non-infringing. A "transformative derivative work" is one that, although based on a copyrighted work, so fundamentally alters it that a new work results. Such a "transformative derivative work" is considered a new work for copyright purposes, and the holder of the copyright of the work from which such a "transformative derivative work" is derived has no rights over it.
Finally, the protections of copyright are subject to one more important limitation: time. Copyrighted works are protected for a set period of time, measured either from the death of their creator or from the date of their creation. After the expiration of that period of time, the copyright protection on the work lapses as the work goes into the "public domain."
Works currently in the public domain include thousands of songs and musical works, novels, poems, stories, and histories written before the twentieth century. Anyone is free to commercially exploit such works by selling copies of those works, creating derivative works based upon them, and by distribuing or displaying the work publicly.