In short. Image alternative text conveys image meaning to assistive technologies and helps Google interpret image subject matter alongside page content and computer vision.

Definition: Image alternative text, often called alt text, is a text equivalent of an image's information or function. For an HTML image element, the alt attribute supplies this alternative so that people using screen readers can access the image's meaning.

Key facts

As of 17 October 2026, Google's image SEO documentation states that Google combines alt text with computer vision and page content to understand an image's subject.
W3C's Images Tutorial bases the text alternative on the image's purpose and context, including whether it conveys information or performs an action.
W3C's decorative images guidance specifies an empty alternative, alt="", for images that add no information to the page.
W3C's complex images guidance pairs a short description with a longer text equivalent for information that exceeds a short phrase or sentence.

How does Google interpret image descriptions?

Google's image SEO guidance gives this example of a descriptive alternative:

<img src="puppy.jpg" alt="Dalmatian puppy playing fetch"/>

The wording identifies the subject and its activity. The same documentation recommends useful descriptions that fit the page context and use relevant keywords appropriately. It warns that filling the attribute with keywords, called keyword stuffing, creates a poor experience and may cause a site to be treated as spam.

Google also draws information from captions, image titles and surrounding page content. It recommends placing images near relevant text. For an image used as a link, its alt text also serves as anchor text, the text associated with the link.

Which alternative fits the image's purpose?

W3C's Images Tutorial recommends a short description of the essential information in an informative image. Context determines the relevant details: its bird example explains that appearance may matter more on a website about birds than on a website about parks.

For a purely decorative image, W3C's decorative images guidance uses an explicitly empty attribute. Its page-border example has this form:

<img src="topinfo_bg.png" alt="">

An omitted attribute can cause some screen readers to announce the filename. The empty value lets assistive technologies ignore the decoration.

For a functional image, such as an image that is the sole content of a link, W3C's functional images guidance describes the destination or action. Its linked logo uses:

<a href="https://www.w3.org/">
  <img src="w3c.png" alt="W3C home">
</a>

The word “home” explains the link's destination. The same guidance uses an empty alternative when adjacent text within the same link already identifies that destination.

How should charts and diagrams be described?

W3C's complex images tutorial separates identification from detailed explanation. A short alternative identifies the image and can indicate where its long description appears. The longer description conveys the information represented visually, including relevant values, scales, relationships and trends.

One documented approach places a text link beside the image that leads to the detailed description on the same page or another page. W3C recommends making long descriptions available to everyone, for example within the main content. Review therefore covers both the image's short alternative and access to its detailed equivalent.

FAQ

Should every image have a written description?

W3C's decorative images guidance recommends alt="" when the image adds no information. You decide whether it is decorative from its purpose and surrounding content.

What should I do with text inside an image?

W3C's Images Tutorial advises avoiding images of text, with an exception for logos. If you use an image of text, its alternative should contain the same words.

Sources

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