Alt Text Isn't Just Accessibility — It's Free SEO Most Creators Skip

The 2026 WebAIM Million report — an annual audit of the top one million home pages — found that 53.1% of sites still ship at least one image with no alt text at all. That's not a niche oversight; it's the majority default, which means the minority who actually write it get a real edge for almost no extra effort.

What alt text is actually doing

Alt text was originally an accessibility feature — a text description a screen reader announces in place of an image, so someone who can't see the photo still knows what's there. That's still its primary job, and it matters on its own: accessibility guidelines require it, and several countries now enforce that legally.

It also does a second job most people miss. Search engines crawl alt text to understand what an image represents, which is how images end up in image search results and adds a relevance signal to the page overall. AI-powered search — Google AI Overviews, Bing Copilot, and similar tools — goes a step further and uses alt text as part of interpreting what an image actually shows, not just indexing it as a file.

The length that actually works

80–140 characters is the sweet spot: enough detail to be genuinely useful to someone using a screen reader, short enough that it doesn't turn into a wall of text they have to sit through before moving on. Write it for a human first — describe what's actually in the image, in plain language — then let relevance follow naturally from an accurate description. Stuffing keywords into alt text reads as spam to both screen reader users and search engines, and it tends to get penalized rather than rewarded.

A useful test: read the alt text out loud without looking at the image. If it tells you what's actually there — not just a vague category, not a keyword list — it's doing its job. "Photo of woman using laptop" is technically alt text; "Woman in a home office reviewing a spreadsheet on a laptop, coffee mug beside the keyboard" actually describes the image.

Multiple images in one post each need their own description

A carousel or multi-image post where every image shares identical alt text (or worse, none at all past the first) wastes the opportunity — each image should describe what's specifically different about it, the same way each slide of a carousel should carry its own distinct point.

Auto-generated alt text is a floor, not a finished product

Instagram and several other platforms now auto-generate basic alt text using image recognition when none is provided manually — a real improvement over nothing, but typically generic ("photo may contain: person, outdoor, tree") compared to a description written with actual context in mind. Relying entirely on auto-generated text misses the more specific, more useful description a person who actually knows what's in the photo — and why it matters — can write in the time it takes to type one sentence.

Decorative images are the one exception

Not every image needs a full descriptive alt text — a purely decorative graphic that adds nothing informational (a plain background pattern, for instance) can use empty alt text specifically so a screen reader skips over it entirely rather than announcing something meaningless. The distinction worth making is whether an image carries actual information a visitor needs, versus one that's purely visual flourish with nothing to describe.

Alt text and captions aren't interchangeable

A caption tells a viewer why an image matters or what it means in context; alt text describes literally what's visually present, for someone who can't see it. Copying a caption directly into the alt field usually misses the actual purpose — a caption might say "best day ever," which describes a feeling, while good alt text says "two people laughing on a beach at sunset," which describes the actual scene. Both serve different, non-overlapping jobs on the same post.

Why this is worth the extra ten seconds per image

Instagram's own SEO guidance now lists alt text alongside hashtags and captions as one of the core things that affects visibility — it's not an optional accessibility checkbox anymore, it's part of how the platform decides what a post is about. Given that the majority of sites and profiles still skip it entirely, writing a real, specific alt text for every image is one of the few remaining actions that's both genuinely helpful to real people and a measurable edge over the average post.