Images have no alt attribute at all

What this means

These images omit the alt attribute entirely, which is NOT the same as alt="". An empty alt="" is the correct, deliberate marking for a decorative image: screen readers skip it silently. A MISSING alt is undeclared intent, so assistive technology falls back to announcing the file name. The legacy images_alt_missing check counts both cases together; this check isolates the omitted-attribute case, which is the one that is always a defect.

How to fix it

Give every image an explicit alt. Describe what the image conveys for meaningful images; use alt="" for purely decorative ones so screen readers skip them on purpose rather than by accident.

Fix effort

This check needs review: the change can be drafted for you, but a person has to approve the wording or choose the target before it ships.

Authoritative source

https://www.w3.org/WAI/tutorials/images/decorative/