For images to be accessible to people who are unable to see them, they must be described using text (if informative) or hidden from assistive technologies (if decorative).
In Canvas, when adding an image to a Canvas page using the rich content editor, you are prompted to enter Alt Text in the Upload Image dialog. Alt text is a short description of the content of the image. It will generally be invisible to sighted users but exposed to people who are using assistive technologies, such as screen readers or Braille displays. If an image fails to load, it will also be displayed to sighted users.
The goal in writing good alt text is to provide equivalent communication to anyone who is unable to see the image. What are you intending to communicate with this image? Express that core idea in the Alt Text field. Alt Text should be succinct, with just enough information to communicate the idea, without burdening the user with unnecessary detail.
Decorative images
If an image is purely decorative, leave the Alt Text field blank, and check the “Decorative Image” checkbox.
Complex images
Alt Text fields are not suitable for long descriptions of complex images such as charts, graphs, or diagrams. Instead, detailed descriptions of these images should be provided elsewhere (e.g., on the same page or on a separate page). See the Images page in our IT Accessibility Checklist for additional information and resources about describing complex images.