Vondran Legal® Copyright Law Insights - What exactly is substantial similarity that leads to potential copyright infringement?

By Attorney Steve® | Vondran Legal®

What Is "Substantial Similarity" in Copyright Law?

One of the biggest misconceptions among artists, designers, authors, software developers, photographers, musicians, filmmakers, and content creators is that copyright infringement only occurs when someone makes an exact copy.

That is not how copyright law works.

In many cases, a person can be liable for copyright infringement even if they never create an identical copy. The real legal question is often whether the defendant copied protected expression to such an extent that the two works are considered substantially similar.

Understanding this concept is critical for creators, businesses, AI developers, Etsy sellers, Amazon merchants, graphic designers, photographers, and software companies.

This guide explains the major factors courts consider when determining substantial similarity and how creators can reduce their legal risk.

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Step One: Copying Must First Be Proven

Before a court even reaches the issue of substantial similarity, the copyright owner generally must establish copying.

Copying is often proven through two forms of evidence:

• Direct evidence (rare)
• Circumstantial evidence

Circumstantial evidence usually consists of:

• The defendant had access to the copyrighted work; and
• The accused work is sufficiently similar to support an inference of copying.

Only after copying has been established does the court determine whether the defendant copied enough protected expression to constitute copyright infringement.

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The Most Important Principle: Copyright Protects Expression—Not Ideas

This is perhaps the single most important rule in copyright law.

Copyright generally protects:

• Original artistic expression
• Original writing
• Creative music
• Original photography
• Original software expression
• Creative selection and arrangement

Copyright generally does not protect:

• Ideas
• Facts
• Historical events
• Common themes
• Public domain material
• Stock scenes (known as scènes à faire)
• Functional concepts
• Methods of operation

This distinction comes directly from the Supreme Court's decision in Feist Publications v. Rural Telephone Service, 499 U.S. 340 (1991).

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General Factors Courts Consider

After filtering out unprotectable material, courts often examine questions such as:

• How much of the work was copied?
• Was the copied material qualitatively important?
• Was the "heart" of the work taken?
• Were the most creative portions copied?
• Is the overall expression substantially similar?
• Are the protected elements similar when viewed together?

Sometimes copying only a small portion of a work can still result in liability if that portion represents the work's most valuable creative expression.

The Supreme Court discussed this concept in Harper & Row Publishers v. Nation Enterprises, 471 U.S. 539 (1985).

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The "Ordinary Observer" Test

Many courts ask a relatively straightforward question:

Would an ordinary observer believe these works are substantially the same?

Rather than conducting a side-by-side microscopic comparison, the analysis often focuses on the overall impression created by the works.

Relevant questions include:

• Do they have the same aesthetic appeal?
• Do they create the same overall impression?
• Would consumers view them as essentially the same work?
• Would ordinary viewers overlook the differences?

Classic cases include:

• Arnstein v. Porter
• Peter Pan Fabrics v. Martin Weiner Corp.

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The "More Discerning" Observer Test

Many creative works combine protected and unprotected material.

For example:

• Historical facts
• Public domain imagery
• Generic characters
• Standard design elements
• Functional components

When that occurs, courts focus only on the protectable creative expression.

This process often requires filtering out:

• Ideas
• Facts
• Public domain content
• Stock elements
• Scènes à faire

The remaining original expression is then compared.

Important cases include:

• Knitwaves, Inc. v. Lollytogs Ltd.
• Boisson v. Banian Ltd.

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The Ninth Circuit's Two-Part Test

The Ninth Circuit—which includes California, Arizona, Nevada, Oregon, Washington, Idaho, Montana, Alaska, and Hawaii—typically applies both an extrinsic test and an intrinsic test.

1. The Extrinsic Test

The extrinsic test is an objective comparison of expressive elements.

Courts may compare:

• Plot
• Themes
• Dialogue
• Mood
• Pace
• Setting
• Characters
• Relationships
• Artistic style
• Structure
• Sequence
• Selection and arrangement
• Visual elements

Expert testimony is often relevant during this phase.

Leading cases include:

• Sid & Marty Krofft Television Productions v. McDonald's Corp.
• Swirsky v. Carey
• Williams v. Gaye

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2. The Intrinsic Test

The intrinsic test is more subjective.

Rather than dissecting individual elements, the question becomes:

Does the accused work capture the same "total concept and feel" as the copyrighted work?

Courts consider:

• Overall artistic impression
• Audience perception
• Emotional impact
• Holistic similarity

The Ninth Circuit's en banc decision in Skidmore v. Led Zeppelin illustrates how courts carefully distinguish between protected musical expression and unprotectable musical building blocks.

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Different Creative Works Require Different Comparisons

Substantial similarity looks different depending on the type of work involved.

Literary Works

Courts may compare:

• Plot structure
• Story arc
• Character development
• Dialogue
• Literary devices
• Narrative progression
• Themes
• Mood
• Pacing

Important cases include:

• Nichols v. Universal Pictures
• Sheldon v. Metro-Goldwyn Pictures

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Characters

Some fictional characters receive copyright protection.

Courts may analyze similarities in:

• Appearance
• Personality
• Speech
• Relationships
• Backstory
• Character development

Examples include:

• DC Comics v. Towle (the Batmobile)
• Warner Bros. v. American Broadcasting

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Music

Music cases can involve highly technical comparisons.

Courts may evaluate:

• Melody
• Harmony
• Rhythm
• Tempo
• Meter
• Chord progression
• Hooks
• Arrangement
• Lyrics
• Signature passages
• Musical motifs

Relevant decisions include:

• Swirsky v. Carey
• Three Boys Music Corp. v. Bolton
• Williams v. Gaye

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Visual Art and Photography

Visual works often require comparisons involving:

• Composition
• Pose
• Perspective
• Lighting
• Camera angle
• Framing
• Subject placement
• Color choices
• Selection and arrangement
• Overall visual impression

Key cases include:

• Rogers v. Koons
• Rentmeester v. Nike

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Software

Software copyright cases frequently analyze:

• Program structure
• Program organization
• Architecture
• User interface
• Menu hierarchy
• Screen displays
• Source code
• Object code
• Selection and arrangement

Important authorities include:

• Computer Associates v. Altai
• Oracle America v. Google

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Compilations and Databases

Not every database is protected.

Instead, courts ask whether there was sufficient originality in the:

• Selection
• Coordination
• Arrangement
• Organization

The Supreme Court's decision in Feist remains the leading authority.

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Derivative Works

Even if someone modifies an existing work, copyright issues may still arise.

Potential derivative works include:

• Sequels
• Adaptations
• Translations
• Character reuse
• Unauthorized recasting
• Works retaining substantial protected expression

Simply changing a few details does not necessarily eliminate infringement risk.

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Willfulness Can Increase Damages

Courts may also consider whether infringement was willful.

Potential evidence includes:

• Destroying evidence
• Concealing copying
• False claims of authorship
• Removing copyright notices
• Ignoring cease-and-desist letters
• Continuing infringement after notice
• Admitting deliberate copying
• Fabricating an independent creation defense

Willful infringement can significantly increase statutory damages under the Copyright Act.

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Practical Tips for Creators

If you are creating original content inspired by existing works:

• Avoid copying the most distinctive creative elements.
• Focus on creating your own expression rather than borrowing someone else's.
• Remember that changing colors, names, or a few details may not be enough.
• Be especially careful with iconic characters, music, photographs, and artwork.
• When in doubt, obtain permission or seek legal advice before commercializing a project.

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Frequently Asked Questions

Is there a percentage of copying that is automatically illegal?

No. Copyright law does not apply a fixed percentage. Courts evaluate both the quantity and the qualitative importance of what was copied.

Are ideas protected?

Generally, no. Copyright protects original expression, not ideas, concepts, methods, or facts.

Can I copy only a small part of a work?

Sometimes even a relatively small portion may infringe if it represents the "heart" or most creative aspect of the original work.

Does changing 20%, 30%, or 50% avoid infringement?

No. There is no "safe percentage" rule. The analysis focuses on whether protected expression remains substantially similar after filtering out unprotectable elements.

Is substantial similarity always decided by a jury?

Not necessarily. While substantial similarity often involves factual issues suitable for a jury, courts may resolve the issue as a matter of law—particularly where no reasonable jury could find substantial similarity under the applicable legal standard.

Does access matter?

Yes. Access to the original work, combined with substantial similarity, is often used to infer copying when direct evidence is unavailable.

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Final Thoughts

Substantial similarity is one of the most nuanced areas of copyright law. The analysis goes far beyond asking whether two works "look alike." Courts focus on whether protected creative expression has been unlawfully appropriated after excluding ideas, facts, public domain material, and other unprotectable elements. Different courts—and different types of works—may require different analytical frameworks.

If you are creating content inspired by existing works, launching a new product, responding to a cease-and-desist letter, or facing a copyright lawsuit, understanding these principles early can help you avoid costly litigation.

Contact Vondran Legal®

Vondran Legal® represents creators, photographers, artists, musicians, software developers, publishers, and businesses nationwide in copyright disputes, substantial similarity analyses, fair use opinions, licensing negotiations, and federal copyright litigation.

Need a copyright risk assessment or substantial similarity opinion? Contact Attorney Steve® to discuss your matter before a dispute becomes a lawsuit.