Canvas Accessibility Checker - Image Errors

Images often support key concepts and enhance learning by providing visual context to your course materials. However, for someone who is blind or has low vision, images can be inaccessible without alternative text (alt text). Alternative text is a short description of an image that is read aloud when a person uses a screen reader. It is also what shows on a page if the image doesn’t load. Alt text should provide all the necessary information a student needs to understand the content and purpose of the image. Here are some key things to remember when adding alternative text to an image:

  • Be concise but descriptive. If an image contains text, the text should be included in the alternative text.  
  • Focus on the context that is relevant to the course. For example, it may be important to describe certain plants and their characteristics in a flower bed in a course about horticulture. But that same image for a landscape architecture course may be focused on the design and features of the flower bed, so the alternative text would describe this instead. 
  • Avoid using phrases such as “image of” or “picture of” because screen readers will already indicate it is an image. 
  • Always end alt text with punctuation so a screen reader will pause after reading it.
  • If an image is decorative and does not have any meaning, you can mark the image as decorative. 

File Name as Alt Text Error 

Canvas will flag two different accessibility issues related to images. Whenever an image is uploaded to Canvas, it will automatically use the file name for the alt text. The Canvas Accessibility Checker will flag the image if the alt text has not been changed from the file name.

Canvas Accessibility Checker highlighting an issue with image alt text, stating that image filenames should not be used as the alt attribute describing the image content.

To fix it, add the appropriate alt text directly in the Canvas Accessibility Checker and then select Apply. 

Screenshot of a Canvas Accessibility Checker demo page with an image of Old Main. The Accessibility Checker panel on the right highlights an issue: "Image filenames should not be used as the alt attribute describing the image content." The below text box has been edited to say "USU's Old Main on a foggy day." Beneath are a checkbox option to mark the image as decorative and a blue button that says apply.

Alt Text Over 120 Characters Error

The other issue the Canvas Accessibility Checker will flag is if the alt text is longer than 120 characters. Unnecessarily long alt text can take away from a screen reader user’s experience if it is too long and detailed. However, there may be times when your alt text needs to be longer than 120 characters to contain all the necessary information. If your image has been flagged with this issue, review the alternative text in the Canvas Accessibility Checker. In the example below, we have a picture of Old Main with lengthy alt text describing many features of Old Main, the surroundings, and more. 

Screenshot of a Canvas Accessibility Checker demo page with an image of Old Main. The Accessibility Checker panel on the right highlights an issue: "Alt text attribute should not contain more than 120 characters." Beneath is a text box with a paragraph-long description of the image.

This can be shortened to something like “USU’s Old Main on a foggy day.” After shortening the alt text, select apply and the changes will be saved. 

If you cannot shorten your alt text without removing important elements of the image, it is okay to keep the alt text you have and ignore this issue.