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All images placed on a digital page must include alt (alternate) text which describes the content or purpose of the image.

Consider the experience of visually-impaired people who are navigating the page using software that vocalizes the content to them.

  • If the image is used as a header, provide alt text that repeats the site or page section name. Alt text (which is required) is not to be confused with other image attributes such as title, caption, or description, which are all optional.
  • If the image is a photograph, describe the subject of the photograph in alt text.
  • If the image contains any text, the alt text should include that text.
  • If the image links to a web page, state the topic of that page in the alt text.
  • If the image contains a great deal of data, ensure that the information is also available in text.

Keep in mind that images should never contain text that is critical to the user's understanding of the content. 

An alternative text will help screen reader users understand the concept, but other user groups do not benefit from alternative texts.

Dyslexic users who use different tools for reading aloud than visually impaired users will not be able to access either the text in the image or the alternative text with their kind of assistive technologies.

In addition, users with low vision who use magnification programs to enlarge elements on the page can experience that the image become pixelated and more difficult to read when enlarged.

References

H30: Providing link text that describes the purpose of a link for anchor elements
H37: Using alt attributes on img elements
F30: Failure of Success Criterion 1.1.1 and 1.2.1 due to using text alternatives that are not alternatives