Alt Text SEO: How Image Descriptions Help Search
Alt text sits at an awkward intersection: it is an accessibility requirement that also happens to be readable by search engines. That makes it tempting to treat as a keyword field. It is not. The sites that get value from alt text treat it as a description first, and the SEO follows.
Here is what alt text actually does for search, how to write it well, and how to tell whether it is working without guessing.
What alt text does for search engines
Search engines can read the pixels of an image well enough to classify a photo, but they cannot reliably read the text inside a chart, the brand on a label, or the reason an image was placed on the page. Alt text supplies that context. It helps a crawler understand the image and, more importantly, the page around it.
Specifically, alt text affects three things:
- Image search indexing. Google Images uses alt text as one signal for what an image depicts. Pages with descriptive alt text are more likely to appear for specific image queries.
- Anchor text for image links. When an image is wrapped in a link, its alt attribute acts like the link’s anchor text. That is a real, if small, signal for the destination page.
- Page context. A page with descriptions that match its topic is easier to classify than the same page with 40 empty alt attributes.
It is not a standalone ranking factor that lifts a page from page three to page one. If an article says “link building is dead” and the image alt says “SEO tips,” the mismatch looks like spam and helps nobody.
What good alt text looks like for SEO
A reliable pattern: describe the subject, add the action or context that matters, and include one distinguishing detail. Keep it under about 125 characters so screen readers do not have to sit through a paragraph. Skip “image of” and “picture of” — assistive technology already announces that it is an image.
| Situation | Weak alt text | Better alt text |
|---|---|---|
| Product photo | product image | Walnut dining table with an oak extension leaf, seats six |
| Team photo | team | Four teammates reviewing a wireframe on a laptop in a bright office |
| Bar chart | chart | Bar chart: mobile revenue grew from $12k to $41k between January and June |
| Screenshot | screenshot | The AltMint review table showing three images with missing alt text and AI suggestions |
| Decorative divider | decorative line | alt="" (empty — let screen readers skip it) |
The distinguishing detail is doing the SEO work, not the keyword. “Walnut dining table” is the subject; “seats six” is what makes it useful to a person comparing tables and to an image search query for a six-seat walnut table.
Alt text vs. title, caption, and file name
These four fields get conflated constantly. They are not interchangeable, and only some of them affect search.
| Field | Who sees it | SEO role |
|---|---|---|
| Alt text | Screen readers; shown when the image fails to load | Context for image search; anchor text for linked images |
| Title attribute | Sometimes a browser tooltip | Not a ranking factor; not a reliable accessibility label |
| Caption | Everyone, when the theme displays it | Indexed page text; useful when it adds information |
| File name | Anyone who inspects the URL | Mild relevance signal; good at upload time, not worth mass renaming |
If you only fix one field, fix alt text. If you have time for two, write captions where they genuinely help the reader — a chart’s source, a product’s dimensions, a photo’s location.
How to show up in image search
- Make images crawlable. Check that the image tags are in the HTML, not injected only by JavaScript after load, and that robots.txt does not block the image files.
- Write the description for the query you want. Not keyword stuffing — describe the thing people would search for. A photo of a finished oak table should say oak, table, and the relevant detail.
- Put images in relevant context. The page copy around the image matters more than the alt text alone. A product page about walnut furniture is a better home for a walnut table photo than a generic “news” post.
- Keep the file size reasonable. Image search favors pages that load well; a 6 MB photo is unlikely to be the result that gets clicked.
- Use structured data where it applies. Product schema with an image URL, article schema with a main image, and a working sitemap all help discovery.
The WordPress image SEO checklist walks through the technical side of these in more detail.
Common alt text SEO myths
“Stuff keywords into every image.” This produces descriptions no person would say, and search engines have seen it for twenty years. It also fails screen reader users, which is the actual requirement.
“Every image needs alt text.” Decorative images should have an empty alt attribute. A description on a spacer image is noise for assistive technology and adds nothing for search.
“Alt text is a direct ranking factor.” Treat it as a supporting signal and an accessibility requirement. The pages that rank for competitive terms usually have good alt text; they also have everything else.
“File names can replace alt text.” A descriptive file name helps a little at upload time, but it is not announced as the image description and does not carry the same context.
How to measure whether alt text is working
Open Search Console, go to Performance, and switch the search type to Images. If your site has descriptive alt text on the images that matter, you should see impressions for specific queries rather than only your brand. Compare a month before and after a cleanup; the change is usually slow and small, but it is measurable.
On the page side, run a Lighthouse accessibility audit before and after. The “image elements do not have alt attributes” count is the clearest number you will get, and it maps directly to the thing you fixed.
For a manual pass, paste a draft into the free alt text checker and see whether it flags file names, redundant phrasing, or missing context. It is a second opinion, not a grader — the final call is whether a person who cannot see the image would understand it.
Is alt text a Google ranking factor?
Google uses alt text to understand images and page context; it is not a standalone ranking boost. It matters most for image search results and for the accessibility of your pages.
How long should alt text be?
Long enough to describe the image, short enough to listen to. Around 5–15 words for most images; up to about 125 characters. Charts and screenshots sometimes need a sentence more.
Should I put keywords in alt text?
Only if they are the natural words for what the image shows. “Walnut dining table, seats six” is fine. A comma-separated keyword list is not.
Does alt text help local SEO?
Indirectly. A photo of a storefront with a description naming the business and the street can reinforce what the page is about, but the page content, business profile, and reviews do the heavy lifting.