Image alt text is the rare on-page SEO factor that's also a WCAG accessibility requirement. Get it right and you serve screen-reader users while sending Google a clear signal about your image content. Get it wrong (or skip it) and you lose ranking opportunities and exclude part of your audience.
What alt text is actually for
The alt attribute on an <img> exists to
describe the image for users who can't see it, screen-reader users, users
with images turned off, and users on flaky connections where the image
fails to load. SEO benefit is a side effect of doing this well,
not the primary purpose.
Google has confirmed alt text is used to understand image content for both image search ranking and as on-page text context. The keyword stuffing tactics from 2008 are now actively penalized.
The rule of thumb
Describe what the image conveys in the context of the page, in plain language, in 50–125 characters. Read your alt text out loud. If it makes sense as a substitute for the image, you're done.
Bad: alt="seo audit tool screenshot best 2026"
Good: alt="AuditAI dashboard showing a 78/100 SEO score with three
critical issues highlighted"
Decorative images: use empty alt
If an image is purely decorative, a divider, a background pattern, an
icon next to text that already says the same thing, use an empty
alt="". Screen readers will skip it. Don't omit the
attribute; without it, some screen readers read the filename
("hero-banner-final-v2-jpg") which is worse than nothing.
alt vs. caption vs. title
- alt: what the image is. Required.
- caption (
<figcaption>), context visible to all users. Use when you want everyone to read it. - title: tooltip on hover. Inconsistent across browsers and invisible on touch devices. Skip it.
Six common mistakes
- Missing alt entirely. The most common WCAG failure on the web. Audit with AuditAI or any accessibility tool.
- Keyword-stuffed alt.
"
seo tools best seo audit free seo", both unhelpful and a spam signal. - Filename as alt. "
IMG_2381" tells nobody anything. - "Image of..." prefix. Screen readers already announce "image", don't repeat it.
- Same alt on every image. Templates that auto-fill "Company logo" on every image, including hero photos, dilute the signal.
- Translated alt that's missing or wrong. If you ship multilingual pages, alt text needs to match the page language.
Functional images: describe the action
If the image is inside an <a> or <button>,
the alt text should describe the destination or action, not the
image itself:
<a href="/cart">
<img src="cart-icon.svg" alt="View shopping cart">
</a>Not alt="shopping cart icon": that tells the screen-reader
user what the icon looks like, but not what tapping it will do.
Charts, diagrams, and infographics
Short alt + long description. Use aria-describedby pointing
to a fuller text version, or include a text summary directly below the
image. The information in a chart shouldn't be locked inside the image.
Automate with care
AI alt-text generation (Microsoft Word, Mac Preview, CMS plugins) gets you 70% of the way there for photos. It does poorly on context, it can tell you "a person at a laptop" but not "Sarah from our customer team demoing AuditAI to a small business owner." Use AI as a draft, then edit.
Cross-reference with our common SEO mistakes guide, missing or weak alt is in the top 10, and the technical SEO checklist covers automated alt-text auditing.