Copyright infringement is a deceptively complex cause of action. It does not lend itself to helpful generalizations because the test for infringement is necessarily vague. This allows for the test to be applied to various types of works and contexts regardless of the nature of the copying. To further complicate copyright infringement actions, different courts have applied the elements of infringement in somewhat conflicting ways, resulting in the creation of exceptions and carve-outs based on the particular facts at hand. As part of the Practice Series, this article provides a brief overview of what is generally regarded as the proper test for infringement without delving into the nuances and conflicts that exist depending on which circuit a court is located in and what type of work is in question.
An action for copyright infringement may arise where a third party violates one or more of the exclusive rights granted to copyright owners. To establish infringement, the plaintiff must prove: “(1) ownership of a valid copyright, and (2) copying of constituent elements of the work that are original.”
Ownership of a valid copyright consists of: “(1) originality in the author; (2) copyrightability of the subject matter; (3) a national point of attachment of the work, such as to permit a claim of copyright; (4) compliance with applicable statutory formalities; and (5) (if the plaintiff is not the author) a transfer of rights or other relationship between the author and the plaintiff so as to constitute the plaintiff as the valid copyright claimant.” A copyright registration certificate from the Copyright Office serves as prima facie evidence of elements (1) through (4). If the defendant rebuts the plaintiff’s prima facie evidence, then the above elements of valid copyright ownership become essential to the plaintiff’s case.
The primary discussion in most copyright infringement cases, and here, is the second element of infringement, namely, the analysis of whether the defendant’s work copies the constituent elements of the plaintiff’s work that are original. This element requires proof: (1) of actual copying of the plaintiff’s work by the defendant and (2) that such copying constitutes an improper appropriation of the plaintiff’s work.
Copying involves a factual question of whether the defendant actually used the plaintiff’s work in order to create his or her own work. It can be proven through direct evidence, such as witness testimony, the defendant’s own admission, or photos or video catching the defendant in the act. More commonly, however, copying is demonstrated, through circumstantial evidence establishing (1) access to the plaintiff’s work and (2) probative similarities between the works. From this evidence, it can be inferred that, given the defendant’s opportunity to copy the plaintiff’s work by having access to it and given certain similarities between the works, it is more likely than not, that the defendant copied the plaintiff’s work.
Access can be proven through evidence that the defendant had a reasonable opportunity to observe the plaintiff’s work. Such proof may consist of showing a particular chain of events through which the defendant may have gained access or establishing that the plaintiff’s work has been widely disseminated. Evidence that the defendant actually observed the plaintiff’s work is not necessary. Such a broad inference of access due to a work’s fame and wide dissemination can be made, in part, because infringement is a strict liability offense. The defendant can still be an infringer even if he or she unintentionally copied the plaintiff’s work. This is true even if the defendant was only subconsciously aware of the work after unknowingly observing it years prior to creating the allegedly infringing work.
In addition to access, it must be proven that the plaintiff’s and defendant’s works share certain probative similarities that collectively help to prove that factual copying has occurred. Proving such similarities serves to negate any claims by the defendant that he or she independently created the allegedly infringing work free from the influence of the plaintiff’s work. Unlike substantial similarities, which are at the heart of the improper appropriation inquiry, probative similarities may be found to exist even in the unoriginal and non-copyrightable components of the plaintiff’s work. The type of similarity that is generally regarded as the most probative of copying is the existence of common errors, whether factual or aesthetic in nature, between the two works. The plaintiff can attempt to prove that the likelihood of such errors occurring independently is too great to be merely a coincidence.
To complicate things further, courts have held that when two works are so strikingly similar as to preclude any reasonable possibility that the defendant’s work was independently created, access may be presumed. To be “striking,” the similarities must be such that they can only be explained through copying, as opposed to independent creation.
Any circumstantial evidence of copying (i.e., proof of access and probative similarities, including the presumption of access created by striking similarities) can, however, be rebutted. This may be accomplished through evidence that the defendant’s work was indeed created independently of the plaintiff’s, especially by showing that the defendant could not reasonably have had access to the plaintiff’s work. Once copying has been proven, it must be established that such copying is actionable.
 Feist Publ’ns, Inc. v. Rural Tel. Serv. Co., 499 U.S. 340, 361 (1991).
 4 Melville B. Nimmer & David Nimmer, Nimmer on Copyright § 13.01[A] (2011).
 See 2 Paul Goldstein, Goldstein on Copyright § 9.1.1 (3d ed. 2011); Marshall A. Leaffer, Understanding Copyright Law 423 (5th ed. 2010); Nimmer, supra note 2, § 13.01[B].
 See Goldstein, supra note 3, § 9.2.2; Leaffer, supra note 3, at 422-23; see also Selle v. Gibb, 741 F.2d 896 (7th Cir. 1984).