Copyright infringement occurs when someone violates one or more of the exclusive rights of a copyright owner without permission. There are three types of infringement: (1) direct infringement, (2) contributory infringement, and (3) vicarious infringement.
The exclusive rights of a copyright owner related to a particular work are (1) the right to reproduce, (2) the right to distribute, (3) the right to make derivative works, (4) the right to publicly display, (5) the right to publicly perform, and (6) in the case of sound recordings, the right to publicly perform by means of a digital audio transmission. 17 U.S.C. §106. Thus, if someone for example captures a picture from a photographer's website, prints out copies and begins to sell them, the person would be liable for copyright infringement because the photographer's exclusive rights to reproduce and distribute the photo would be violated.
Generally, a plaintiff proves direct copyright infringement by showing (1) ownership of a valid copyright and (2) that the defendant copied the work (or violated one of the plaintiff's exclusive rights as a copyright owner). However, in most cases evidence of direct copying will not be available, so courts use the two-part "substantial similarity test" in which a plaintiff can establish copying by showing that (1) the infringer had access to the work and (2) the two works are substantially similar. The defendants in these cases are known as "direct infringers."
Access can be shown by either (1) establishing a causal link proving that the defendant had access to the work, or (2) widespread dissemination of the work. Failure to prove access may be overcome by showing that the two works are so "strikingly similar" that access may be presumed.
To prove substantial similarity, courts apply an extrinsic test that compares the individual elements of the two works to find specific similarities between them, and the intrinsic test, which looks for similarities from the viewpoint of an "ordinary and reasonable observer" taking into account the "total concept and feel of the works."
With regards to proving the first element of direct copyright infringement, ownership of a valid copyright, courts require that a plaintiff produce a certificate of registration before a copyright infringement case can proceed. 17 U.S.C. §411.
Unlike direct infringement, contributory copyright infringement is not based on a statute but rather on tort law. A contributory infringer is someone who induces, causes, or materially contributes to the infringing conduct of another person or entity. The contributory infringer must also have knowledge of the infringement. Contributory infringement was one of the types of copyright infringement at issue in the Napster case (A&M Records, Inc. v Napster; Inc. (9th Cir 2001) 239 F3d 1004, 1019).
Vicarious copyright infringement is based on the agency principle of respondeat superior, i.e., the employer-employee relationship, but may be shown even in the absence of such a relationship. A vicarious infringer is a person or company that (1) has the right and ability to control the acts of the direct infringer, and (2) has a direct financial interest in the infringing act. Vicarious infringement was one of the types of copyright infringement at issue in the Grokster case (Metro-Goldwyn-Mayer Studios, Inc. v Grokster, Ltd. (2005) 545 US 913, 930, 125 S Ct 2764).
There are several defenses to copyright infringement. First, a defendant can assert a statute of limitations defense if the infringement suit was brought more than 3 years after the claim accrued. 17 USC §507(b). The defense of laches, a long delay in asserting a claim that has prejudiced the defendant, can also be asserted. In certain circumstances a defendant may be able to assert that an implied license exists between the parties as evidenced from the plaintiff's conduct, thus making the alleged infringing behavior non-infringing.