WCAG 1.1.1: Non-text Content
WCAG 1.1.1 Non-text Content is a level A success criterion from WCAG 2.0. Images, icons and other non-text content need a text alternative that serves the same purpose. Decorative images can have an empty alt so assistive technology skips them.
People using screen readers never see the picture, only the alternative.
How to test
List every image and icon. Check that informative ones have alt text that matches the purpose, and decorative ones use empty alt.
How to fix
Write the alt from the job the image does: name a product, describe a chart, or leave it empty if the nearby text already says it.
Example that fails
A product photo with no alt, so the buy link is announced as an empty image.
Example that passes the check
The same photo uses alt text 'Stoneware mug, moss green'.
Shopify
On each product, edit the media alt so it is the product name plus a variant detail. In the theme, do not overwrite that alt with the file name.
WooCommerce
Set the image alt in the Media Library and confirm the product template prints it on the shop loop and the single product.
WordPress
Select the Image block and fill Alternative text. Featured images take their alt from the Media Library.
Wix
Select the image in the Editor and write the alt in the image settings. Do not leave the uploaded file name.