Alt text and captions describe images, but they serve different audiences. Alt text is invisible HTML — it lives inside the alt attribute and is read aloud by screen readers, parsed by search engines, and used by AI assistants. Captions are visible text that sits next to an image, usually inside a <figcaption> element, and are read by everyone who can see the page.

The two aren't interchangeable, and they aren't redundant. Most images need one or the other; some images need both. This guide shows you which is which.

Quick Answer

• Always write alt text. Every image needs the alt attribute, even if it's empty.
• Add a caption when sighted readers benefit from extra context — credits, attribution, a clarifying note, or expanded context.
• Don't repeat the alt text in the caption. Screen readers will hear both, which is annoying.

What Each One Does

Alt text

Alt text is the value of the HTML alt attribute on an <img>:

<img src="pasta.jpg" alt="Bowl of cacio e pepe with cracked black pepper">

It's invisible to sighted readers in a normal page render. Screen readers like JAWS, NVDA, and VoiceOver read it out loud. Search engines use it to understand and rank the image. AI assistants read it to decide whether to cite your page when answering visual queries. For a complete primer, see What Is Alt Text?.

Caption

A caption is visible text — typically wrapped in <figcaption> inside a <figure> element:

<figure>
  <img src="pasta.jpg" alt="Bowl of cacio e pepe with cracked black pepper">
  <figcaption>Photo by Sam Kean for The Roman Kitchen, used with permission.</figcaption>
</figure>

Sighted readers see it. Screen readers read it after the alt text. Search engines see it as part of the page text — they don't treat it as a separate signal the way they treat alt text.

When to Use Each

Alt text only

Most images on most sites need alt text only. Product photos, hero images, blog post imagery, screenshots, icons that convey meaning. The image speaks for itself; the alt text translates it for the audiences who can't see it.

Caption only

Decorative images that need a visible attribution credit, but don't add information for screen reader users. Set alt="" and put the credit in the caption.

Both

News photos, editorial images, infographics, and historical photos often deserve both. The alt text describes what's in the image; the caption adds context that sighted readers want.

<figure>
  <img src="protest.jpg" alt="Crowd of about 200 people marching with signs in front of city hall, late afternoon light">
  <figcaption>Protest at City Hall, March 14, 2026. Photo: Maya Patel.</figcaption>
</figure>

The alt text describes what's visible. The caption adds the time, location, and credit — context the screen reader user wouldn't otherwise have.

Don't Duplicate

The most common mistake is writing the same description in both the alt text and the caption. A screen reader user hears: "Crowd of about 200 people marching with signs in front of city hall. Crowd of about 200 people marching with signs in front of city hall." Twice. It's irritating and unnecessary.

Pick one to carry the description, and use the other for complementary information.

SEO Impact

Search engines treat alt text and captions differently. Alt text is a strong signal — it tells Google what an image is about, and it's used to rank images in Google Image Search. Captions are part of the page text — they help with general page ranking but don't carry the same weight for image search specifically.

For ranking strategy, see Alt Text for SEO in 2026: 9 Rules That Move Rankings.

What About the Title Attribute?

The HTML title attribute (which renders as a tooltip on hover) is sometimes confused with alt text and captions. It's neither — and it's mostly unreliable. See Alt Text vs Title Attribute for the full breakdown.

Next Steps

Most sites have hundreds of images that need alt text but no captions — and that's fine. The first job is making sure every image has alt text. Run a free crawl to see how many of your images are missing it. For larger catalogs, automating alt text generation is the only way to keep up — see AltText.ai pricing.