Add alt text to images in Squarespace

• Image blocks: edit the page, click the image block's pencil icon, and fill in Image alt text on the Content tab.
• Gallery sections (7.1): click an image in the gallery editor and add a Description. Note that it becomes both the alt text and a visible caption.
• Gallery blocks: click the gear on an image and enter an image title (used as alt text).
• Product images: hover over the image, click the three dots, choose Edit metadata, and fill in Alt text. If it's empty, the product name is used.

Section background images can't have alt text. If a background image carries meaning, use an image block instead.

Check it: publish your change, then run a new scan from your dashboard. The issue should drop off the list.