On a site with hundreds of images, writing alt text is tedious, which is why it is usually missing. Hand the job to an AI and every field fills in within minutes. As a drafting step this is a good use of the tool. But filled in and correct are different states, so it is worth knowing what you are reviewing for before you start.
What alt text is actually for
Alt text is a sentence that delivers, to someone who cannot see the image, the information that image was carrying. It is not “the picture rendered as words”. That distinction is the whole subject.
The same photograph has different correct answers depending on where it sits. A shopfront photo on a how to find us page wants “white building with a blue awning; the entrance is on the side street” — because that is what the reader came to the picture for. The identical photo used as atmosphere at the top of an about page carries no information, so empty alt text is the correct answer.
This is the box an AI cannot fill in principle. The model looks at a picture and describes the picture. Why that picture is on this page is known only to the person who put it there. Deciding that a decorative image deserves empty alt text is a judgement it will never reach, because there is always something in front of it to describe.
Getting a draft worth having
None of which makes the draft worthless. Supplying context with the request cuts the editing dramatically. Do not send the image alone: say which page it is on, what the surrounding copy says, and whether the image is decorative or informative.
Specify the format too. Alt text has a handful of standard mistakes, and the prompt can head most of them off.
Review by priority, not exhaustively
Re-reading several hundred entries is not realistic. Splitting them by priority makes it feasible. Informative images — charts, maps, screenshots, product detail — get reviewed in full. Decorative images get empty alt text in bulk with a spot check. Everything ambiguous in between is worked through in order of page views.
Finally, alt text is where accessibility starts rather than where it finishes. Heading structure, link wording, visible focus and colour contrast all have to be in place before a screen reader user can genuinely use the page. A site with perfect alt text and nothing else is still hard work.
Working through the accessibility checklist in order is covered in the accessibility series, and other uses of AI for review and classification live in the AI archive. If you would like the state of a whole site assessed at once, a diagnostic is part of our optimization program.