To understand the importance of digital watermarks for images and audio files on the Internet, it is vital to know how copyright law protects them.

U.S. copyright law originates from the Constitution, which provides that "Congress shall have power . . . to promote the progress of science and useful arts, by securing for limited times to authors and inventors the exclusive right to their respective writings and discoveries." Today, a large body of statutory and case law outlines the boundaries of copyright protection. The relevant statute provides that copyright protection subsists "in original works of authorship fixed in any tangible medium of expression, now known or later developed, from which they can be perceived, reproduced, or otherwise communicated, either directly or with the aid of a machine or device." Among other original works of authorship specifically listed by Congress in the statute are "pictorial," "graphic," and "audiovisual" works, as well as "sound recordings."

What is the purpose of copyright law? As explained by the then-top official at the U.S. Copyright Office, "In essence, copyright is the right of an author to control the reproduction of his intellectual creation." Thus, once an author creates a copyrightable work, the author owns the exclusive right to determine who may reproduce the work, or do or authorize others to do certain things with the work (at least for a limited time as provided in the law).

Although, as in many areas of the law, copyright is complicated by an extensive set of rules and frequent uncertainty, the basic premise of copyright law is quite simple. When a person or business reproduces a copyrightable work without the owner's permission, that person or business may subject itself to liability for copyright infringement. The examples are endless and appear in everyday life: A movie producer uses material from the author of a novel in his movie without obtaining the writer's permission; an advertising agency uses a photograph in a magazine ad for one of its clients even though the photographer did not authorize its use; an enterprising teenager makes copies of a popular musical cassette tape on his home stereo and sells copies on a busy street corner; a corporation purchases one copy of a useful but expensive word processing program and makes copies of it for use on multiple computers in its offices. Although some violations are more blatant than others, they each may amount to copyright infringement. (Note that numerous aspects of copyright law are beyond the scope of this article, including the requirement that a work possesses "originality" to qualify for protection, that works are protected only for limited times and may thereafter fall into the "public domain," and that some copyrighted works may be reproduced under "fair use" guidelines.)

It has long been recognized that graphic images and sound recordings are protected by copyright. While GIFs and WAV files obviously did not exist when the Founding Fathers drafted the Constitution -- or even in 1976, when Congress drafted the current version of the U.S. Copyright Act -- it seems clear that these World Wide Web file types are proper subjects of copyright law. GIFs and other graphic image file types are akin to photographs, drawings, logos or other pictorial or graphic works that are recognized by statute and by case law. Similarly, WAV and other audio file types are most likely sound recordings, which are recognized expressly by the Copyright Act. Because copyright law applies to works "fixed in any tangible medium of expression, now known or later developed," Internet images and audio files clearly seem to be protected by copyright law, which anticipates the introduction of new technologies and does not need to be redrafted to accommodate them. Copyright law in the United States has proven itself remarkably adaptable to new technologies that did not exist when the laws were written. As the U.S. Supreme Court said in addressing copyright infringement and video cassette recorders in 1984: "From its beginning, the law of copyright has developed in response to significant changes in technology."

Once protected by copyright, the law prohibits others from reproducing a work without the author's permission. Thus, a webmaster who includes on a client's site audio from a commercial CD or a photograph or an icon from another web site without obtaining permission from the songwriter, photographer or artist (such as by a written license or assurance that the work is in the public domain) may infringe another's copyright and subject himself to liability.

While complicated by the facts of any particular case, the elements required by a plaintiff to prove copyright infringement are minimal. In general, a copyright owner need only prove that (1) he owns the copyright in the work, and (2) the defendant copied the work. The second element is often established by showing that a defendant had access to the copyrighted work and that the copy is "substantially similar" to the original.