Success Criterion 1.1.1 (Non-text Content) is the WCAG rule most people mean when they say a site "needs alt text". It is a Level A criterion — the baseline, not an advanced nicety — and it is usually the first thing an accessibility audit or a screen reader user hits.
Every piece of non-text content (in practice, almost always an image) needs a text alternative that serves the same purpose. That's the whole rule. The nuance is entirely in "same purpose":
| Image type | What 1.1.1 requires |
|---|---|
| Informative (a product photo, a chart, a screenshot) | Alt text that describes what the image conveys, concise, no "image of" prefix. |
| Decorative (a background flourish, a spacer, a repeated icon next to visible text) | alt="" — an empty attribute, not a missing one. This tells assistive tech to
skip it entirely. |
| Functional (an image inside a link or button with no other label) | Alt text describing the action or destination, e.g. alt="Download the report (PDF)",
not the image itself. |
| Complex (a chart, a diagram) | Short alt text plus a longer text description nearby or linked, since alt text alone can't carry the full data. |
alt attribute at all. Screen readers fall back to reading the
filename, e.g. "IMG dash 4021 dash final dot jpg".alt="" (hides real content).1.1.1 failures are mechanically detectable (a crawler can tell you exactly which
<img> tags have no alt attribute) and they are the most common failure on the
median website, which is why they are usually the first item on any WCAG audit or legal-risk
scan.
Want to know where your own site stands? A live scan checks up to 10 public pages for free, no login required:
For the full picture — every image, every page, with alt text already written — see the Alt Text Audit.