Alt Text in PDFs

When alternative text is required, when it is not, and what WCAG actually says.

PDF alt text is essential for accessibility, but it is often misunderstood and incorrectly applied, leading to inaccessible documents even when images appear compliant.

In practice, most images in documents are decorative and should not be announced by screen readers. This article explains how alt text works in PDFs, when it is required, and when images should be marked as decorative.

What alt text is meant to do

Alt text provides a text alternative for images so that users who cannot see them can understand their purpose or meaning.

The goal of alt text is not to describe images visually. The goal is to convey information that would otherwise be lost.

If no information is lost by ignoring the image, alt text is usually not required.

What WCAG actually requires

WCAG addresses alt text in Success Criterion 1.1.1 (Non-text Content).

WCAG states that:

“All non-text content that is presented to the user has a text alternative that serves the equivalent purpose.”

WCAG also explicitly allows exceptions. The same criterion states that text alternatives are not required for non-text content that is:

“Purely decorative, used only for visual formatting, or not presented to users.”

This distinction is critical and often overlooked.

When alt text is required in PDFs

Alt text is required when an image conveys information that a user needs in order to understand the content.

In PDFs, alt text is typically required for:

  • Charts and graphs

  • Diagrams and flowcharts

  • Screenshots used as instructions

  • Images that convey data, trends, or comparisons

  • Icons that communicate meaning without accompanying text

If removing the image would cause loss of information, alt text is required.

When alt text is NOT required

Alt text is not required when an image does not convey meaningful information.

Common examples include:

  • Decorative icons

  • Visual separators or dividers

  • Background images

  • Repeated logos that do not add information

  • Stock imagery used for aesthetics

  • Icons next to text that already conveys the same meaning

In these cases, the image should be marked as decorative so it is ignored by assistive technologies.

Providing alt text for decorative images creates unnecessary verbosity and reduces usability for screen reader users.

Why most images are decorative in practice

In real-world documents, the majority of images exist to support layout, branding, or visual interest.

Most PDFs contain:

  • Decorative icons

  • Logos

  • Background elements

  • Visual accents

  • Repeated imagery with no new information

Very few images actually convey unique information. Typically, only charts, graphs, and instructional visuals require alt text.

Recognizing this distinction is key to producing accessible documents that are usable, not noisy.

Alt text in PDFs is not the same as alt text in HTML

Alt text in PDFs depends on proper tagging and structure.

In PDFs:

  • Alt text is attached to tagged content

  • Decorative images must be explicitly marked as artifacts

  • Incorrect tagging can expose decorative content to screen readers

  • Automated tools often mis-handle image tagging

This is why simply “adding alt text” without reviewing the PDF structure often results in accessibility failures.

Why overusing alt text harms accessibility

When decorative images include alt text, screen reader users are forced to listen to unnecessary descriptions that interrupt reading flow.

This creates:

  • Cognitive overload

  • Slower navigation

  • Frustration for users

Accessibility is about usability, not completeness. Correctly excluding decorative images is just as important as providing alt text where it is needed.

How alt text is evaluated during accessibility testing

During accessibility testing, reviewers typically check:

  • Whether informative images have meaningful alt text

  • Whether decorative images are properly hidden

  • Whether alt text matches the purpose of the image

  • Whether complex images are adequately described

Both missing alt text and unnecessary alt text can result in accessibility failures.

Conclusion

Alt text is required only when images convey information. Most images in PDFs are decorative and should not be announced to screen reader users.

Understanding when alt text is needed—and when it is not—is essential for producing accessible PDFs that are clear, efficient, and usable.

Accessibility Testing Note

Alt text and decorative image handling are commonly reviewed during PDF accessibility testing to ensure compliance with WCAG requirements and usability for assistive technology users.