Ten image types, each with the mistakes people make and a version that works. The context line matters: change where an image sits and the right alt changes with it.
Context: Shop page for the teapot
Weak
Better
Sage-green ceramic teapot with a bamboo handle, 1 litreColour, material and the handle are what a shopper compares. The capacity is on the label, so it belongs in alt too.
Context: Article about commuting by bike in winter
Weak
Better
Cyclist in a yellow rain jacket crossing a wet cobblestone bridge at duskThe rain, the cobbles and the dusk are the article's point: commuting in bad conditions. "Image of" is dropped.
Context: Local-food feature
Weak
Better
Stallholder arranging crates of figs and apricots at a morning marketDescribes the action and setting without guessing age, ethnicity or name.
Weak
Better
Acme homeThe image is the link, so its alt is the link name. Say where it goes. An empty alt here leaves the link nameless.
Weak
Better
SearchDescribe the action. The shape of the icon doesn't matter to someone who can't see it.
Weak
Better
alt=""It adds nothing. Use alt="" so screen readers skip it. A missing attribute is not the same: the file name may be read.
Weak
Better
Summer sale: 30% off all teapots until 31 AugustThe words are the content. Transcribe them.
Weak
Better
Bar chart: online sales rose each quarter of 2026, from 18% to 41% of revenue. Data table below.Type + key takeaway in alt; the full numbers go in a table or long description.
A diagram of the Moon's phases is the extreme case: the picture is the explanation, and alt can only point to it. Compare how ahaboo talks a listener through why the Moon changes shape, using narration where a caption would fall short.
Weak
Better
Screenshot: Settings > Display, with the Dark mode toggle switched onHere the medium matters, and so does the one control the reader needs to find.
Weak
Better
alt=""The name is already in the adjacent text. alt="" avoids repeating it. If the photo adds something (e.g. "in her pottery studio"), a short alt with only that is fine.
Automated checks catch mechanical mistakes only. For a fresh draft from the image itself, use the AI alt text generator; for the rules, see best practices.
For a product page: "Sage-green ceramic teapot with a bamboo handle, 1 litre". It is specific, names what a shopper compares, and skips "image of". For the same image as page decoration, the right alt is empty (alt="").
File names ("IMG_4031.jpg"), single generic words ("teapot", "logo"), "image of…" openers, and keyword lists ("teapot green teapot buy teapot"). All four are common and all four fail users.
Use the organisation name. If the logo is a link to the home page, describe the destination, such as "Acme home". Add "logo" only when being a logo matters, for example on a sponsors page.
A short alt naming the chart type and its main takeaway, plus the detailed data in a table or long description nearby, as W3C WAI recommends for complex images.