These three get lumped together constantly — understandably, since they’re all “text near an image.” But they serve different purposes, have very different SEO weight, and mixing them up usually means one of them gets neglected entirely. Here’s what actually separates them.
The three, defined
Alt text lives in the HTML alt attribute. It’s invisible on the page itself — read aloud by screen readers, displayed only if the image fails to load, and used by search engines to understand the image’s content.
<img src="mug.jpg" alt="Handmade blue ceramic mug on a wooden table">Title attribute is a tooltip that appears when a user hovers over an image (in browsers that still support hover, which increasingly excludes mobile entirely). It’s set via the title attribute, separate from alt.
<img src="mug.jpg" alt="Handmade blue ceramic mug" title="Our bestselling mug, glazed in cobalt blue">Caption is visible text displayed on the page, usually directly below or beside the image. Unlike the other two, it’s regular page content — readable by everyone, not an HTML attribute at all.
<figure>
<img src="mug.jpg" alt="Handmade blue ceramic mug on a wooden table">
<figcaption>Our bestselling cobalt blue mug, hand-thrown in small batches.</figcaption>
</figure>Side-by-side comparison
| Alt text | Title attribute | Caption | |
|---|---|---|---|
| Visible on page | No | Only on hover | Yes, always |
| Read by screen readers | Yes | Sometimes, inconsistently | Yes, as regular text |
| SEO weight | Meaningful — used for image understanding and image search | Minimal — a weak, secondary signal at best | Indirect — read as page content, not tied to the image specifically |
| Required by HTML standards | Effectively yes, for accessibility | No | No |
| Best use case | Every meaningful image | Supplementary detail, rarely necessary | Adding visible context or credit for human readers |
Why alt text carries the most SEO weight
Of the three, alt text is the one search engines lean on most directly to understand what an image actually shows — it’s the closest thing to a direct description in the page’s code. Title attributes, by contrast, are inconsistently read by assistive technology and don’t carry comparable weight; treat them as a nice-to-have for desktop hover context, not a ranking lever. Search Engine Journal’s overview of alt text fundamentals is a good reference if you want the full breakdown of how the two attributes differ in practice.
Captions sit in a different category entirely. Because they’re visible body text, search engines read and index them like any other content on the page — which means a caption can reinforce a page’s topic, but it isn’t doing the same job as alt text. A blind reader using a screen reader still won’t get any information about the image itself from a caption alone, since screen readers announce captions as regular text, separate from the image element.
A common mistake: treating them as interchangeable
The most frequent error isn’t getting any one of these wrong — it’s assuming that having one means you don’t need the others. A beautifully written caption doesn’t make alt text optional; a screen reader user tabbing through an image still needs the alt attribute to know what’s there, caption or not. Likewise, a detailed title attribute doesn’t substitute for alt text either, since title attributes are inconsistently supported and many users will never see or hear it at all.
The practical takeaway: write alt text for every meaningful image, full stop. Add a caption when there’s genuinely useful visible context to share with all readers. Reserve the title attribute for rare cases — supplementary detail that doesn’t fit naturally into either of the other two.
Where to go from here
Since alt text is the one doing the real SEO and accessibility work, getting it right matters more than the other two combined. If you haven’t already, our full guide to writing alt text that actually helps SEO covers the specific rules, a decision framework for different image types, and real before/after examples.
This post is part of a series on image SEO. Start with the overview: Are Alt Tags Important for SEO? Or continue to: How to Write Alt Text That Works · 7 Alt Text Mistakes Hurting Your SEO · How to Audit and Fix Alt Text