Writing alt text for images that actually does its job

Alt text has two real audiences. One is a person using a screen reader or a browser with images disabled. The other is a search engine trying to understand what a page contains. The same short, accurate description serves both of them well. Most alt text on small-business sites serves neither. It is either left blank on images that carry real information, or stuffed with a keyword phrase that has little to do with what the image actually shows.

What alt text (alternative text) is actually for a screen reader

The alt attribute exists to convey, to someone who cannot see the image, whatever information the image itself was contributing to the page. If a photo shows a tradesperson repairing a specific type of appliance, the alt text should say that, in plain language. That is the information a sighted visitor gets from glancing at the image. The same photo might instead be purely decorative — a background texture, a repeated pattern with no informational content. In that case the correct alt text is an empty attribute, not a strained description of a picture that was never meant to convey anything.

Getting this distinction wrong in either direction causes a real problem. Leaving an informative image blank means a screen reader user gets nothing where a sighted visitor got real information. Describing a decorative image forces a screen reader to announce something with no purpose. It adds noise, not removes it.

What good alt text actually says, and how it should describe the image — an example

Good alt text is short, specific, and describes what the image conveys. It is not a caption, not a keyword phrase, and not a restatement of the surrounding heading. “A licensed electrician installing a switchboard in a residential meter box” tells a screen reader user what a sighted visitor sees. “Electrician Brisbane switchboard installation cheap” tells them nothing usable, and reads exactly as what it is to a search engine as well.

What alt text should do	What it commonly does instead
Describe what the image conveys, in plain language	Restate a target keyword phrase regardless of what the image shows
Stay concise — a sentence, not a paragraph	Either be left entirely blank on an informative image, or padded unnecessarily
Use an empty attribute for purely decorative images	Force a description onto an image that was never meant to carry information
Match what a sighted visitor actually sees	Describe an idealised or generic version of the image rather than the actual one
Skip “image of” or “picture of” — the alt attribute already implies that	Start every entry with the same redundant phrase

Where alt text and decorative images sit inside a page’s accessibility

Alt text is one specific, checkable item among the broader set of things that determine whether a page is usable by someone relying on assistive technology — alongside semantic headings, keyboard operability and sufficient colour contrast. It is one of the easier items to get right, because it can be reviewed image by image rather than requiring a full technical audit. That makes it a reasonable starting point for a business wanting to improve accessibility without a full review. Where a fuller picture of a site’s accessibility position is useful, the accessibility self-assessment tool works through the broader set of questions a business can check itself, alongside what an automated scan can and cannot actually confirm.

Alt text on images from a shoot or a stock library

Alt text is written after the image exists, so it depends on the image actually showing what it is supposed to show. A photograph that was properly briefed in the first place is far easier to write accurate alt text for than a stock image standing in for something it does not actually depict. Photography briefs covers planning a shoot around the pages and information a photo needs to carry — the upstream decision alt text has to describe honestly, whatever it ends up saying.

Complex images and how screen readers announce charts, diagrams and screenshots

A photograph is usually straightforward to describe in a sentence. A chart, diagram or screenshot carrying real information is not. The alt attribute alone is rarely enough space to convey what the image shows. Where an image carries data or a process a reader genuinely needs, the more reliable approach is a short alt description naming what the image is. Pair it with the same information written out in the surrounding text — a table, a list, or a paragraph that does not depend on the image to be understood. That way, the information survives for a reader who cannot see the image at all, rather than being lost entirely because it only existed inside a graphic.

A quick way to check existing alt text

Browsing a page with images disabled, or using a browser’s accessibility inspector to list every image’s alt attribute at once, quickly surfaces both failure modes on an existing site. Images can have no alt text at all, or alt text stuffed with a keyword phrase unrelated to what the image shows. Either is a fast, low-cost fix once identified. Correcting alt text requires no design or development change — only a more accurate sentence in a field that already exists.

What to do next: writing alt text for a photograph, a painting, or a screenshot

Go through a page’s images and write, for each one, the one plain sentence a sighted visitor would use to describe what it shows to someone on the phone. If an image is purely decorative, set its alt attribute empty rather than inventing a description for it. That single pass through a page’s existing images is usually a short task, and it is one of the few accessibility improvements that requires no design or development change to apply.