What is image alt text and why it is not just for accessibility - Zephyra Studio

Alt text is a short description of an image that lives in the code and is not visible on the page. Screen readers read it aloud to blind and low-vision users, and it appears when an image fails to load. Google uses it as a substitute for what the algorithm cannot see, so together with the file name and surrounding text it helps the image make sense in image search. Good alt text is not keyword stuffing. It is one sentence saying what is in the image and why it is there.

What alt text actually is, and what it is not

Alt text is the value of the alt attribute in the HTML image tag: <img src="..." alt="...">. If an image is purely decorative, such as a background texture, alt should be empty (alt=""), because that tells a screen reader to skip it.

It is not visible to a visitor. A screen reader sees it, Google sees it, and anyone whose image fails to load on a weak connection sees it. So it has to make sense outside the image itself.

Why it matters beyond accessibility

Google cannot look at an image the way a person does, so alt text, the file name, and the text around the image help it classify the image. That is why images with good alt text have a chance to appear in Google image search.

There is a concrete reason too: if an image carries information written nowhere else on the page, such as a price in a screenshot or words inside an infographic, alt is the only place Google and a screen reader can get that information.

How to write it: a concrete example

An example of badly written alt text: alt="image, site, development, affordable". That is a string of words with no structure, telling neither a person nor an algorithm what is in the image.

The same image written properly: alt="Page load speed before and after optimisation, 4.2 seconds before and 1.1 seconds after". This describes what the image shows and carries numbers nobody could read if the image were unavailable.

A short rule: if someone read the page through alt texts alone, would they understand what it is about? If not, the alt texts are too weak.

Common mistakes

Three mistakes repeat. First: the same alt text on every image, or alt that just repeats the file name ("IMG_4532.jpg"). Second: stuffing keywords unrelated to the image, which Google recognises as manipulation. Third: omitting alt entirely, which is the worst for both accessibility and image search.

If an image repeats several times on the same page, such as a logo in the header and footer, the first can carry the full description while the others can use a short or empty alt so a screen reader does not repeat itself.

Related terms

For the wider picture, see also:

Source

Key takeaways

• Alt text describes an image in the code, read by screen readers and Google.
• It is not keyword stuffing, but one sentence about what is in the image.
• Decorative images get an empty alt (alt=""), not a missing attribute.
• If an image carries unique information, alt is the only place search can read it.

Conclusion

Alt texts are one of the quickest fixes on a site: no redesign needed, just a few hours going through the media library. If you want a technical review of the whole site along with the fix, our SEO optimisation covers accessibility and image search as part of the same job.