What this test checks
This test checks whether images in the PDF document provide an alternative or Alt text.
Why this maybe a barrier
An alternative text provides a semantic description of the image which is often essential to understand the context of the image and the references to it in the document, otherwise assistive technology users, especially the visually impaired, would lose important semantic context.
Screen readers cannot convey the purpose of images without such text. Users relying on assistive technologies may miss important information, thus drastically affecting their comprehension of the document.
WCAG 2.2 Technique
This check is related to the WCAG 2.2 technique → PDF1: Applying text alternatives to images with the Alt entry in PDF documents.
WCAG 2.2 Success Criterion
1.1.1 Non-text Content (Level A) — "All non-text content that is presented to the user has a text alternative that serves the equivalent purpose, except for the situations listed below.
- Controls, Input
- Time-Based Media
- Test
- Sensory
- CAPTCHA
- Decoration, Formatting, Invisible"
Fore more information, visit WCAG 2.2 Success Criterion 1.1.1 under the guideline Text Alternatives.
PDF/UA Principle
Section 7.3: Graphics — "If text represented in a graphic is not text in a natural language that is meant to be read by a human reader, alternative text describing the nature or purpose of the graphic shall be provided."
The implementation uses Matterhorn protocol checkpoint namely 13-004:
13-004 — <Figure> tag alternative or replacement text missing.