What Is Alt Text? (And Does It Actually Help SEO?)

Alt text is the alt attribute on an image — a short written description of what it shows. Its main job is accessibility: screen readers read it aloud to people who cannot see the image. It does help SEO, by making images eligible for Google Images and, when the image is a link, by acting as that link's anchor text.

What it looks like

<img src="/blog/img/anchor-text-chart.jpg"
     alt="Bar chart showing branded anchors making up 62% of a natural backlink profile" />

That is the whole feature. One attribute, one sentence. It is displayed on screen only when the image fails to load, which is why so many sites have gone years without noticing theirs are empty.

The primary purpose is accessibility, not SEO

This matters for how you write it. Alt text exists because the World Health Organization estimates at least 2.2 billion people have a near or distance vision impairment, and a screen reader encountering an image with no alt attribute announces the filename — IMG_4471.jpg — or nothing at all.

It is also a legal requirement in many contexts. WCAG 2.1 success criterion 1.1.1 (Non-text Content) requires a text alternative for every non-decorative image, and WCAG is the standard referenced by the ADA in the US, the European Accessibility Act, and equivalent legislation elsewhere. Missing alt text is one of the most commonly cited failures in accessibility audits and in the web accessibility lawsuits that follow them.

The useful consequence: if you write alt text properly for a blind user, you have automatically written it correctly for Google. Every piece of SEO advice below falls out of that one principle. WebAIM's guide to alternative text is the best free reference if you want the accessibility side in depth.

How Google actually uses it

Google's image SEO documentation is direct about it. Alt text, together with the filename, tells Google what an image depicts — computer vision has come a long way, but a written description is still the strongest signal available. Google also warns explicitly that filling alt attributes with keywords is a poor experience for users and can make a site look like spam.

Concretely, alt text does four things:

It gets images into Google Images. Image search is a meaningful traffic source in visual niches — recipes, products, design, travel — and alt text is the primary way Google understands what to index a picture as.

It adds topical context to the page. Not a large signal, but a real one. A page with images described as "cast iron skillet searing a ribeye" reinforces what the page is about.

It powers the image results shown inside AI answers. AI Overviews and Perplexity both surface images alongside text answers, and they select those images using the same descriptive signals.

It becomes the anchor text when the image is a link. This is the one worth its own section.

The part link builders should care about

Google's documentation states plainly that when you use an image as a link, its alt text serves the role anchor text plays for a text link.

That means an image link is not the anchor-text-free freebie people assume. Wrap a logo in a link with alt="" and you have handed Google a link with no anchor text at all. Wrap it with alt="cheap backlinks buy links fast" and you have built an exact-match anchor as aggressive as any text link — with all the anchor text over-optimization risk that carries.

Three practical implications:

Audit the alt text on your linked images, not just your text anchors. A footer badge, an award logo or a partner button repeated site-wide can quietly skew your anchor profile.
When you get an image link — a sponsor badge, a directory listing, a "featured in" logo — the alt text is negotiable, and most people never think to ask. Requesting a natural, descriptive alt is free.
Descriptive beats exact-match, exactly as it does for text links. alt="Backlinkster logo" is a branded anchor, and branded anchors are what natural profiles are mostly made of.

If you are working out which image links are worth pursuing in the first place, do image links pass SEO value covers how they compare to text links.

How to write good alt text

Describe the image, in context. The right description depends on why the image is on the page. A photo of a chart on a data post needs the chart's finding: "Line chart showing organic traffic rising from 400 to 3,100 sessions over six months." The same photo in a gallery of screenshots might just need "Google Analytics traffic report."

Keep it under about 125 characters. Older screen readers truncate around there, and a description longer than a sentence usually means the image needs a caption instead.

Skip "image of" and "picture of." Screen readers already announce that it is an image. Starting with those words wastes the first two words of every description.

Include the keyword only if it genuinely describes the image. If your page targets "link exchange" and the image shows two site owners swapping links, say so. If the image is a stock photo of a laptop, do not force it in.

Give decorative images an empty alt. alt="" is correct and deliberate — it tells a screen reader to skip the image entirely. Dividers, background flourishes and spacer graphics should all have it. This is not the same as omitting the attribute, which makes the screen reader fall back to reading the filename.

Never leave the attribute off entirely. Every <img> should have an alt, even if it is empty.

Alt text vs. the things people confuse it with

Attribute	Who sees it	Does it help SEO?
`alt`	Screen readers; shown if the image fails to load	Yes — image indexing, page context, anchor text on image links
`title`	Sighted users, as a tooltip on hover	No. Inconsistently exposed to screen readers; usually best left off
Caption (`<figcaption>`)	Everyone, visibly on the page	Yes — visible text Google reads normally, and read far more often than alt text
Filename	Nobody, in normal use	Minor. `red-cast-iron-skillet.jpg` beats `IMG_4471.jpg`

The one to stop using is title. It adds a tooltip that mobile users never see, is announced unreliably by assistive technology, and is frequently used to duplicate the alt text for no benefit.

Common mistakes

Bulk-generating alt text from the page's target keyword. Twelve images on a page all described as "link building strategy" is keyword stuffing, and it is trivially detectable.
Leaving CMS defaults in place. Many platforms auto-populate alt with the filename or the post title. Both are worse than nothing.
Describing images inside text-heavy screenshots literally. If the screenshot's content matters, transcribe the key point rather than saying "screenshot of a dashboard."
Treating alt text as a ranking lever. It is a small signal on a normal page. Image weight and loading behaviour affect Core Web Vitals far more than alt text affects rankings.
Ignoring images inserted by page builders. Background images set in CSS have no alt attribute at all; if they carry meaning, they should be real <img> elements.

Frequently asked questions

Does alt text help SEO? Yes, modestly and in specific ways. It makes images eligible to rank in Google Images, gives Google context about the page, and — when the image is wrapped in a link — functions as that link's anchor text. It is not a significant ranking factor for the page itself.

How long should alt text be? Under about 125 characters. That is where older screen readers truncate, and it is long enough for one clear descriptive sentence. If you need more, the information belongs in a caption or in the body text, where everyone can read it.

Should every image have alt text? Every image should have an alt attribute, but not every image needs a description. Informative images get a real description; purely decorative images get alt="", which tells screen readers to skip them. Omitting the attribute entirely is the only wrong option.

Is alt text the same as anchor text? Not normally — but when an image is used as a link, Google treats its alt text the way it treats anchor text on a text link. That makes alt text on linked images part of your anchor text profile, and worth auditing alongside your text anchors.

Does keyword stuffing alt text work? No. Google's image documentation names it specifically as something that creates a bad user experience and can cause a site to be seen as spam. Alt text describing an image accurately outperforms alt text stuffed with target terms.

Do AI image generators and AI search care about alt text? AI answer engines use alt text as one signal for selecting images to display alongside answers, and it helps them understand what a page contains. As with search, an accurate description does more than a keyword-loaded one.

The bottom line

Write alt text for the person who cannot see the image, and the SEO takes care of itself. Describe what is actually there, keep it to a sentence, use alt="" on decoration, and drop the title attribute. Then check one thing most sites never check: the alt text on every image you have wrapped in a link, because that text is functioning as anchor text whether you intended it or not.

Speaking of anchors — the links pointing at your site are still what moves rankings, and controlling their anchor text is half the work. Backlinkster runs one-for-one in-content swaps with owners of related sites, each verified live by code, so the anchor sits in a real sentence rather than a footer badge. See the plans.