Short answer: Alt text is a short description of an image, written in its alt attribute. Screen readers read it aloud, and Google uses it with what it sees in the image and the text of the page to understand the image. Describe what the image shows in context, in a short phrase or one or two sentences. Google finds images in img elements, not in CSS backgrounds, and also reads the file name and the page around the image.
Alt text and how Google uses it
Screen readers read alt text to people who are blind or have low vision, and it also helps people on slow connections.
For Google, alt text is the most important attribute for giving more information about an image. Google uses it along with computer vision and the content of the page to understand what the image is about. When an image is a link, its alt text works as the link’s anchor text.
Google also warns against filling alt text with keywords: it makes a bad experience and may get your site seen as spam.
From Google Search Central, “Image SEO best practices”, and Google’s technical writing course, “Write helpful alt text”, read November 2, 2026.
How to write alt text
Google’s course on alt text says to describe the image in the context of the text around it: the same photo can need different alt text on two pages. Keep it to a short phrase or one or two sentences, because long descriptions interrupt people using screen readers.
Leave out words like “Image of” or “Photo of”. Start with a capital letter and end with a period, so screen readers pause before the text that follows. Don’t write it in all caps, since screen readers can read capitals as acronyms.
Some images need an empty alt, written alt="": a decorative image, or one that only repeats what the text next to it already says. Screen readers skip an empty alt. With no alt at all, screen readers read the file name aloud instead.
| The alt text | What happens |
|---|---|
| None | Google lists it as bad. Screen readers read the file name aloud |
| A list of keywords, such as “puppy dog baby dog pup pups…” | Bad: keyword stuffing, which may get the site seen as spam |
| “puppy” | Better, but it says little |
| “Dalmatian puppy playing fetch” | Best: what the photo shows, in a few words |
| Empty, alt="" | Right for a decorative image or one that repeats the text next to it. Screen readers skip it |
Rows 1 to 4 are Google’s own example in “Image SEO best practices”; row 5 comes from “Write helpful alt text”.
How to optimize an image for Google
- Put the image in an img element with a src, not in a CSS background. Google doesn’t index CSS images.
- Name the file with a few words that say what it shows: my-new-black-kitten.jpg beats IMG00023.JPG. On pages in another language, translate the file name too.
- Use a format Google supports: BMP, GIF, JPEG, PNG, WebP, SVG or AVIF, with an extension that matches the file type.
- Keep it sharp but light. Compress it, and give each screen a size that fits with srcset, keeping a src as the fallback.
- Write the alt text: what the image shows on this page, in a short phrase, or an empty alt if it is decorative.
- Place the image near the text it illustrates, on a page about the same subject. A caption helps.
- Mark your preferred image for the page with og:image or schema.org’s primaryImageOfPage, which can influence the one Google shows. Pick a relevant, high-resolution photo, not your logo.
If the same image appears on many pages, use the same URL everywhere so Google can cache it and reuse it. An image sitemap helps Google find images it might otherwise miss. The page’s title and description count too, which our guide on meta descriptions and SEO titles covers. For the photos on your Google profile, see our guide on Business Profile photos.
From Google Search Central, “Image SEO best practices”.
What we found on our own site
On November 2, 2026, we checked every image on the 214 public pages of our site, 1,370 image tags in all. None was missing its alt attribute. Of the 458 with an empty alt, 428 were the dark-mode copy of our logo, hidden from screen readers so they don’t read our name twice.
Another 24 were decorative images at the top of our home page. The other six were photos that needed a description. On our home page, a setting took the alt from a field that was empty on all our articles, so the newest article’s cover had none in either language. On our content marketing page, an example photo shown twice per language had no alt in the media library. We fixed both that afternoon.
The share images of our guides have a file name in each language, such as local-citations-photo-share-en.webp and citaciones-locales-foto-compartir-es.webp, and alt text in each language.
Before you publish an image
- The image is an img element with a src, not a CSS background.
- The file name says what the image shows, in the language of the page.
- The format is one Google supports, and the file is compressed.
- The alt text describes the image in context, in a short phrase or one or two sentences.
- Decorative images, and images that repeat the text next to them, have an empty alt.
- The page’s share image is a relevant photo, not your logo.
RememberWrite alt text for people: what the image shows, in context, in a few words. Leave it empty on decorative images, never stuff it with keywords, and give Google a real img element with a descriptive file name.
If you want us to check the images and the rest of your site, see our technical SEO service.
Quick answers about alt text and image SEO
What is alt text?
Alt text, or alternative text, is a short description of an image written in its alt attribute. Screen readers read it aloud for people who are blind or have low vision, and Google uses it to understand what the image shows.
Does alt text help SEO?
Yes. Google calls alt text the most important attribute for giving more information about an image, and uses it with computer vision and the page content to understand the image. Filling it with keywords works against you: Google says that can get your site seen as spam.
How long should alt text be?
Google’s course on alt text asks for a short phrase or one or two sentences, because long descriptions interrupt people who use screen readers. If an image needs more, such as a chart, describe it in the text of the page.
Does every image need alt text?
Every image needs an alt attribute, but not every one needs words in it. A decorative image, or one that repeats the text beside it, gets an empty alt so screen readers skip it. Without any alt, screen readers read the file name aloud.
Does the image file name matter for SEO?
A little. Google says the file name gives very light clues about what the image shows. Use a short, descriptive name, such as my-new-black-kitten.jpg rather than IMG00023.JPG, and translate it on pages in other languages.
Sources
All read on November 2, 2026: Google Search Central, Image SEO best practices, and Google’s technical writing course, Write helpful alt text. Our own case: a check of every image on our public pages on November 2, 2026.