Alt text is a short written description attached to an image (the HTML `alt` attribute) that a screen reader announces in place of the picture, so people who cannot see it still get the information it conveys.

Which WCAG rule requires alt text?

WCAG 2.2 Success Criterion 1.1.1 (Non-text Content), Level A. Because it is the most basic conformance level, failing it undermines almost any accessibility claim.

What alt text should a decorative image have?

An empty `alt` attribute. That tells assistive technology the image carries no information and can be skipped, instead of reading out a filename. Never omit the attribute entirely.

Can automated tools catch every missing alt text problem?

Automated scanning reliably flags images with no `alt` attribute, but it cannot judge whether existing alt text is accurate or meaningful — that still needs human review. AllyProof reports the missing cases and points you to the ones a person should check.

Common Violations

Missing Alt Text: The Most-Cited Accessibility Violation

An <img> tag with no alt attribute (or an <input type="image"> with no alt text) has no way to tell a screen reader what the image shows. Sighted users see the picture; everyone using assistive technology gets either silence or, worse, the raw image filename read aloud ("IMG-2847-final-v3.jpg").

This is the single most frequently cited issue in ADA web accessibility lawsuits — industry data puts it at roughly 89% of complaints, well ahead of every other violation type. It's also one of the easiest to fix, which is part of why it's so often flagged: it's a checklist item, not a judgment call.

Why it matters

Non-text content that conveys information — product photos, charts, icons that act as buttons, scanned documents — has to have a text equivalent, or that information simply doesn't exist for a portion of your visitors. This is WCAG Success Criterion 1.1.1 (Non-text Content), a Level A requirement, meaning it sits in the baseline every conformance level requires.

How to fix it

Meaningful images need a specific, concise description of what the image communicates — not what it literally depicts.

<!-- Before -->
<img src="q3-revenue-chart.png">

<!-- After -->
<img src="q3-revenue-chart.png" alt="Q3 revenue grew 18% year over year, reaching $4.2M">

Purely decorative images (a background flourish, a spacer, an icon that's redundant with adjacent visible text) should use an empty alt="" — this explicitly tells assistive technology to skip the image, which is the correct outcome. An empty alt is not a mistake; a missing alt attribute is.

<!-- A decorative icon next to visible text that already says "Download" -->
<img src="download-icon.svg" alt="">
Download

Image buttons (<input type="image">, or an <img> wrapped in a clickable element with no other text) need alt text describing the action, not the image: alt="Submit search", not alt="Magnifying glass icon".

What good alt text is not

Avoid alt text that just repeats the filename, says "image of..." or "picture of..." (screen readers already announce that it's an image), or crams in keywords for SEO — none of that helps the person actually trying to understand the content.

Automated scanners like AllyProof can reliably detect a missing alt attribute, but they can't judge whether the alt text you wrote is actually a good description — that's a Category B "partially automatable" check. Treat a passing scan as "every image has alt text," not "every image has good alt text."

Official references

Common questions

What is alt text?: Alt text is a short written description attached to an image (the HTML `alt` attribute) that a screen reader announces in place of the picture, so people who cannot see it still get the information it conveys.
Which WCAG rule requires alt text?: WCAG 2.2 Success Criterion 1.1.1 (Non-text Content), Level A. Because it is the most basic conformance level, failing it undermines almost any accessibility claim.
What alt text should a decorative image have?: An empty `alt` attribute. That tells assistive technology the image carries no information and can be skipped, instead of reading out a filename. Never omit the attribute entirely.
Can automated tools catch every missing alt text problem?: Automated scanning reliably flags images with no `alt` attribute, but it cannot judge whether existing alt text is accurate or meaningful — that still needs human review. AllyProof reports the missing cases and points you to the ones a person should check.

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