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Image Alt Text: Accessibility and SEO Done Right
A practical guide to image alt text: what it is for, how to write it, when an image is decorative, and how it feeds accessibility and image search.
Run a fresh DomainLens audit and use the report as your priority list.
What alt text is for
The alt attribute is a short text description of an image. Its primary job is accessibility: a screen reader reads it aloud so a blind or low-vision user knows what the image shows. It is also shown when the image fails to load, and it gives search engines the context they cannot get from the pixels — which is how it doubles as an SEO signal.
So alt text serves real people first and crawlers second. The good news is that writing it for a person who cannot see the image almost always produces exactly what search engines want too: a clear, honest description of what is there.
How to write good alt text
- Describe what the image shows and why it is on the page, in a natural sentence or phrase.
- Keep it concise — roughly a short sentence; screen readers read the whole thing.
- Include a relevant keyword only if it genuinely describes the image; never stuff terms.
- For images that are also links, describe where the link goes, since the alt text becomes the link’s accessible name.
- Do not start with "image of" or "picture of" — the screen reader already announces it is an image.
Decorative vs meaningful images
Not every image needs a description. A meaningful image (a product photo, a chart, an infographic) needs alt text that conveys its information. A purely decorative image (a background flourish, a divider, an icon next to text that already says the same thing) should have an empty alt attribute: alt="".
The empty alt is deliberate, not a mistake — it tells screen readers to skip the image instead of announcing a filename or reading redundant text. Omitting the attribute entirely is worse, because some screen readers then fall back to reading the file name aloud.
Alt text and image search
Google Images is a real traffic source, and alt text is one of the main signals it uses to understand an image, alongside the file name, surrounding text, and structured data. Descriptive alt text and sensible file names (running-shoes-blue.jpg, not IMG_4821.jpg) make your images eligible to rank for relevant image queries.
It is not a keyword lever, though. The images that rank are the ones that are genuinely relevant, well-described, and on a fast, crawlable page — the same fundamentals as the rest of SEO.
Common alt text mistakes
- Missing alt attributes on meaningful images, so screen readers and search engines get nothing.
- Keyword-stuffed alt text that reads as spam and hurts the accessibility experience.
- Using the file name (IMG_4821.jpg) as the effective description by leaving alt off entirely.
- Writing alt text for decorative images instead of using alt="" to skip them.
- Describing a linked image by its appearance instead of its destination.
How DomainLens checks alt text
DomainLens scans the rendered images on the page and reports those missing an alt attribute, so you can see at a glance which meaningful images are invisible to screen readers and search engines.
Use the finding as a prompt to review, not to auto-fill: add descriptions to the images that carry meaning, mark the decorative ones as alt="", and you improve accessibility and image SEO in the same pass.