Credibility · 22 points
Image alt text
One check, stated three ways: what we measure, what would make it wrong, and how to confirm it yourself.
What this measures
How many <img> elements exist, how many carry an alt attribute, and whether the text is a real description. alt="" counts as handled: it is the correct way to mark decorative art. A filename used as alt does not.
Where this check can be wrong
CSS background images and inline SVG are invisible to this check, so a page can score well and still be unreadable to a screen reader.
Verify it without taking our word for it
curl -s https://your.site | grep -o '<img[^>]*>' — and read each one without looking at the picture.