Images Concepts

Images must have text alternatives that describe the information or function represented in the images. This ensures that images can be used by people with various disabilities. This tutorial demonstrates how to provide appropriate text alternatives based on the purpose of the image:

  • Informative images: Images that graphically illustrate concepts and information, typically pictures and illustrations. The text alternative should be at least a short description conveying the essential information presented by the image.

  • Decorative images: If the only purpose of an image is to add visual interest to the page, rather than to convey information that is important to understanding the page, the text alternative should be null (alt="").

  • Functional images: The text alternative of an image used as a link or as a button should describe the functionality of the link or button rather than the visual image. Examples for such images are a printer icon to represent the print function or a button to submit of a form.

  • Images of text: Readable text is sometimes presented within an image. If the image is not a logo, text in images should be avoided. However, if images of text are used, the text alternative should contain the same words as in the image.

  • Complex images such as graphs and diagrams: To convey data or detailed information, the text alternative should be a full text equivalent of the data or information provided in the image.

  • Groups of images: If multiple images convey a single piece of information, the text alternative for one image should convey the information conveyed by the entire group.

  • Image maps: The text alternative for an image that contains multiple clickable areas should provide an overall context for the set of links. In addition, each individual clickable area should have alternative text that describes the purpose or destination of the link.

For quick overview on deciding which category a specific image fits into, see the An alt Decision Tree.

Why is this important?

Images are used extensively on websites and can create major barriers when they are not accessible. Accessible images prove to be beneficial in many situations such as:

  • People using screen readers: The text alternative can be read aloud or rendered as Braille
  • People using speech input software: Users can put the focus onto a button or linked image with a single voice command
  • People browsing speech-enabled websites: The text alternative can be read aloud
  • Mobile web users: Images can be turned off, especially for data-roaming
  • Search engine optimization: Images become indexable by search engines

Note: Images are often important for communicating information and interacting with web pages. Illustrations make it much easier to understand information for certain types of learners. Some people who enlarge web pages use images as cues for orientation. Removing images from websites (so called “text-only versions”) makes websites less accessible for these users.

Success Criteria:

  • 1.1.1 Non-text Content: All non-text content that is presented to the user has a text alternative that serves the equivalent purpose, except for the situations listed[…]. (Level A)

  • 1.4.5 Images of Text: If the technologies being used can achieve the visual presentation, text is used to convey information rather than images of text except [for customizable and essential images] (Level AA)

  • 1.4.9 Images of Text (No Exception): Images of text are only used for pure decoration or where a particular presentation of text is essential to the information being conveyed (Level AAA)