Non-text Content
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.
In plain language
Every image, icon, or other non-text element must have a text description that explains what it shows or what it's for.
Why it matters
Screen reader users can only access text — they can't see images directly. If an image has no text alternative, they have no way to know what it shows, whether it's an important photo, a button, or a chart full of data.
In practice
Fails this criterion
A "buy now" button is just a shopping cart icon with no text alternative. A screen reader announces only "button," giving no clue what it does.
Meets this criterion
The same icon has a text alternative like "Add to cart," which the screen reader reads aloud. Purely decorative images are marked so screen readers skip over them instead of announcing meaningless filenames.
Test it yourself
Inspect the images on a page (browser dev tools, or a screen reader) and check their alt text. Ask yourself: if I couldn't see this image, would this text tell me what it shows or what it does?