Proving Copyright Infringement

By Hank FasthoffJuly 4, 2026

A copyright infringement claim requires proof of two things. First, the plaintiff must own a valid copyright in the work. Second, the defendant must have copied protectable elements of that work. Both elements must be established before a court reaches the question of remedies, and both involve layers of analysis that determine whether a claim survives a motion to dismiss, survives summary judgment, and ultimately prevails at trial.

Ownership of a Valid Copyright

Ownership requires an original work fixed in a tangible medium of expression. 17 U.S.C. § 102(a). Originality under copyright law demands only that the work be independently created and possess a minimal degree of creativity. Feist Publications, Inc. v. Rural Telephone Service Co., 499 U.S. 340, 345 (1991). A certificate of registration issued within five years of first publication constitutes prima facie evidence of the validity of the copyright and of the facts stated in the certificate, including authorship and ownership. 17 U.S.C. § 410(c). After five years, the evidentiary weight of the certificate is within the court's discretion.

Registration is also a prerequisite to filing suit. Under 17 U.S.C. § 411(a), as interpreted in Fourth Estate Public Benefit Corp. v. Wall-Street.com, LLC, 586 U.S. 296 (2019), a copyright owner can't bring an infringement action until the Copyright Office has issued a registration or refused one. An owner who discovers infringement but has not yet registered must apply, wait for the Copyright Office to act, and only then file suit. Special handling can expedite the process to approximately five business days for an additional $800 fee.

Proving Copying

Direct evidence of copying is rare. A plaintiff occasionally obtains an admission or a document showing that the defendant had access to the plaintiff's work and used it as a source, but most cases rely on circumstantial proof. Under the framework established in Arnstein v. Porter, 154 F.2d 464 (2d Cir. 1946), and refined by subsequent decisions across the circuits, a plaintiff proves copying through two steps.

First, the plaintiff must prove that the defendant copied the plaintiff's work, as opposed to creating a similar work independently. Actual copying is typically established by showing that the defendant had access to the plaintiff's work and that the two works share probative similarities, meaning similarities that wouldn't be expected to arise if the works were created independently. Probative similarity is a factual question. Courts may consider expert testimony and dissection of the works at this stage, and the similarities need not involve protectable expression. Probative similarity establishes that copying occurred; it doesn't establish that the copying is actionable.

Second, the plaintiff must prove that the defendant copied enough protectable expression to constitute unlawful appropriation. This is the substantial similarity inquiry, and it's where infringement cases are won or lost.

Substantial Similarity

Substantial similarity asks whether the defendant's work is similar enough, in its protectable expression, to the plaintiff's work that the copying constitutes infringement. Federal circuits apply different tests, though all require the plaintiff to show similarity of protected expression rather than similarity of ideas, facts, or other unprotectable elements.

In the Second Circuit and circuits following its approach (including the Fifth Circuit), courts apply the ordinary observer test. Under Peter Pan Fabrics, Inc. v. Martin Weiner Corp., 274 F.2d 487, 489 (2d Cir. 1960), two works are substantially similar if an ordinary observer, unless setting out to detect the disparities, would be disposed to overlook them and regard the aesthetic appeal of the works as the same. When a work contains both protectable and unprotectable elements, courts in these circuits apply a more discerning ordinary observer test, which requires separating the protectable elements from the unprotectable ones and comparing only the protectable expression.

In the Ninth Circuit, courts apply a two-part extrinsic/intrinsic test. Under Sid & Marty Krofft Television Productions, Inc. v. McDonald's Corp., 562 F.2d 1157 (9th Cir. 1977), and its progeny, the extrinsic test objectively analyzes the specific expressive elements of the two works, often with the assistance of expert testimony. If the works share objective similarities in protectable expression, the intrinsic test then asks whether an ordinary reasonable person would find the total concept and feel of the two works to be substantially similar. Summary judgment for the defendant is appropriate if the works fail the extrinsic test, even if a lay observer might perceive the works as similar.

For computer programs, several circuits apply an abstraction-filtration-comparison test. In Computer Associates International, Inc. v. Altai, Inc., 982 F.2d 693 (2d Cir. 1992), the Second Circuit held that a court must first abstract the program into its structural parts, then filter out unprotectable elements (ideas, elements dictated by efficiency, elements dictated by external factors, and elements taken from the public domain), and then compare what remains with the allegedly infringing program.

Ideas, Facts, and Other Unprotectable Elements

Copyright protects expression fixed in a tangible medium, but not ideas, facts, procedures, processes, systems, methods of operation, concepts, principles, or discoveries. 17 U.S.C. § 102(b). An infringement analysis must separate protectable expression from unprotectable elements before comparing the two works.

Under the merger doctrine, when an idea can be expressed in only one or a limited number of ways, the expression merges with the idea and isn't protectable. A competitor who expresses the same idea in the same way hasn't infringed, because protecting that expression would confer a monopoly on the underlying idea.

Under the scènes à faire doctrine, elements of a work that are standard, stock, or common to a particular genre or subject aren't protectable. A courtroom drama that includes a judge, a jury, opening statements, and cross-examination uses scènes à faire that are available to all authors. A competitor who includes the same stock elements has copied ideas, not protectable expression.

Secondary Liability

Copyright infringement need not be direct. A party can face secondary liability under two theories, contributory infringement and vicarious infringement, each with distinct elements.

Contributory infringement, as the Supreme Court most recently defined it in Cox Communications, Inc. v. Sony Music Entertainment, No. 24-171 (U.S. Mar. 25, 2026), requires that a party intended its service to be used for infringement. That intent can be shown in two ways. First, the plaintiff can prove that the defendant induced infringement through affirmative steps to encourage it, the theory the Court recognized in Metro-Goldwyn-Mayer Studios Inc. v. Grokster, Ltd., 545 U.S. 913 (2005). Second, the plaintiff can prove that the defendant provided a service tailored to infringement, meaning a service not capable of substantial or commercially significant noninfringing uses. Before Cox, some lower courts had applied a broader standard under which knowledge of infringing activity combined with a material contribution to it was sufficient. Cox rejected that formulation, holding that a company isn't liable for merely providing a general-purpose service with knowledge that some users will infringe.

Under the vicarious infringement theory, a party with the right and ability to supervise the infringing activity and a direct financial interest in it may be liable even without knowledge of the infringing activity. Vicarious liability is a strict liability doctrine rooted in respondeat superior. It applies to employers, landlords, and platform operators who profit from infringement they had the power to stop.

Defenses

Below are some of the defenses available to a copyright infringement defendant:

• Independent creation: Copyright protects against copying, not against independent creation of a similar work. If the defendant can prove that it created its work without access to or knowledge of the plaintiff's work, there's no infringement even if the works are identical. Sheldon v. Metro-Goldwyn Pictures Corp., 81 F.2d 49 (2d Cir. 1936) (L. Hand, J.).
• Fair use: Section 107 of the Copyright Act provides that the fair use of a copyrighted work for purposes such as criticism, comment, news reporting, teaching, scholarship, or research isn't infringement. Fair use is determined by weighing four statutory factors, and recent Supreme Court decisions including Andy Warhol Foundation for the Visual Arts, Inc. v. Goldsmith, 598 U.S. 508 (2023), have refined how courts assess transformative use and commercial purpose. A separate article in this series addresses fair use in detail.
• Implied license: When a copyright owner creates a work at another's request, delivers it, and intends the requesting party to use it, courts may find an implied nonexclusive license even without a written agreement. Effects Associates, Inc. v. Cohen, 908 F.2d 555 (9th Cir. 1990). An implied license is narrow. It typically covers only the use the parties contemplated, and unless the licensee paid for it, it can be revoked.
• First sale doctrine: Under 17 U.S.C. § 109(a), the owner of a lawfully made copy of a copyrighted work may sell or otherwise dispose of that copy without the copyright owner's permission. Section 109(c) also permits the owner of a lawfully made copy to display it publicly to viewers present at the place where the copy is located. First sale limits the distribution and display rights in these specific ways but doesn't affect the reproduction or performance rights.
• Statute of limitations: Under 17 U.S.C. § 507(b), a copyright infringement action must be commenced within three years after the claim accrued. Most circuits apply a discovery rule under which a claim accrues when the plaintiff discovers, or with due diligence should have discovered, the infringement. In Warner Chappell Music, Inc. v. Nealy, 601 U.S. 366 (2024), the Supreme Court held that a copyright owner who files a timely claim under the discovery rule may recover damages for infringement that occurred more than three years before the lawsuit was filed. The Court assumed without deciding, however, that the discovery rule applies to copyright claims, leaving that threshold question unresolved.
• Laches: In Petrella v. Metro-Goldwyn-Mayer, Inc., 572 U.S. 663 (2014), the Supreme Court held that laches can't bar a copyright infringement claim filed within the statutory limitations period. However, the Court noted that unreasonable delay may be relevant to the equitable relief a court awards.
• Copyright misuse: A defendant may assert that the plaintiff misused its copyright by extending it beyond its lawful scope, such as requiring exclusive use or restricting competition in an unrelated market. Copyright misuse is an equitable defense that renders the copyright unenforceable during the period of misuse.

When a Case Is Worth Bringing

Registration status controls the economic calculus of every infringement claim. An owner who registered before infringement began, or within three months of first publication, can recover statutory damages of $750 to $30,000 per work, and up to $150,000 per work for willful infringement, under 17 U.S.C. § 504(c) and attorney's fees under 17 U.S.C. § 505. An owner who registered late is limited to actual damages and the infringer's profits under § 504(b), both of which require proof and are often modest relative to the cost of federal litigation.

Before bringing a claim, a plaintiff should evaluate several practical questions. Is the copyright registered, and was the registration timely? Can access be proved, or does the claim depend on striking similarity? Is the allegedly copied material protectable expression, or is it ideas, facts, scènes à faire, or functional elements that copyright doesn't reach? Is there a fair use defense, and how strong is it? What are the actual damages, and do they justify the cost of litigation?

A claim with timely registration, provable access, and substantial similarity in protectable expression creates settlement pressure and can be litigated economically. A claim without timely registration, with disputed access, and where the similarities exist primarily in unprotectable elements is very expensive to bring and can be difficult to win. Evaluating these factors before filing, rather than after discovery, is what separates viable infringement claims from cases that consume resources without potential for producing results.