Writing image alt text for people, not for search

Aug 29
3 min read

Updated: 4 days ago

Introduction

An audit reports three hundred images without alt text. Somebody works through them adding the company name and a service keyword to each one, and the report turns green.

Nothing has been improved. The purpose of alt text is to describe an image to somebody who cannot see it, and a list of keywords describes nothing. Written properly it serves people using screen readers, it appears when an image fails to load, and it happens to give search engines an accurate account of the picture — but only when it is written for the first purpose.

1. Writing image alt text means describing what is in the picture

The definition that resolves most confusion.

Say what the image shows, plainly, as you would describe it to somebody on the telephone. If the description would make sense read aloud in place of the image, it is correct, and no further optimisation is needed or useful.

2. Write for somebody who cannot see it

The audience that determines the wording.

A person using a screen reader hears this text in the flow of the page. Keyword lists, file names and the company name repeated three hundred times make the page harder to use, which is the opposite of what the attribute exists for.

3. Keep it short and specific

Length works against it.

A sentence is usually enough, and long descriptions become tedious when heard rather than read. Specific detail beats length: naming what is happening and who is in the picture communicates more than a paragraph of general description.

4. Leave decorative images empty

An instruction rather than an omission.

Background patterns, dividers and purely decorative graphics should carry an empty alt attribute, so screen readers skip them. This is different from having no attribute at all, and it makes pages significantly less tiring to listen to.

5. Describe function for images that do something

The case people get wrong most often.

If an image is a link or a button, the alt text should say what it does rather than what it looks like. A magnifying glass icon should be described as search, not as a magnifying glass, because the function is what the listener needs.

6. Do not begin with image of

Redundant in every case.

Screen readers already announce that an image is present. Starting the text with a phrase saying so repeats information the listener already has, which is a small irritation multiplied across every image on the site.

7. Include text that appears within the image

Otherwise the content is lost entirely.

Prices, opening hours, offers and instructions set inside a graphic exist nowhere else on the page. The alt text must carry that information, and ideally the page should carry it as real text as well.

8. Use the keyword only when it is accurate

Where search and accessibility genuinely align.

If the image genuinely shows the thing the page is about, naming it is both accurate and helpful. Inserting a term because the page targets it, when the picture shows something else, is misleading in exactly the way the attribute is designed to prevent.

9. Add it at the point of upload

The only sustainable approach.

Retrospective projects to caption three hundred images rarely finish. Making it part of how images are added means the problem stops growing, and the backlog can then be worked through in priority order over time.

Prioritise the backlog rather than attempting all of it. Images on your main service and product pages, and any image carrying information that appears nowhere else, are worth doing first; a decorative photograph in a six-year-old article can wait indefinitely or be marked decorative in bulk.

Conclusion

Write alt text as a description for somebody who cannot see the image, because that is what makes it useful and accurate.

Keep it short and specific rather than long, give decorative images an empty attribute so they are skipped, describe the function rather than the appearance for images that act as links or buttons, drop redundant openings, carry any text shown inside the image into the description, include the keyword only where it genuinely describes the picture, add it when images are uploaded, and work through the existing backlog in priority order.