Images and Diagrams Accessibility

What 

Update/create accessible Images and Diagrams by adding alt text.  All images should have alt text OR be marked as decorative.  Alt text should be no longer than 120-140 characters (the size of a Tweet).  For more information and examples, keep reading. 

Why  

Adding alt text provides text explanations for users with visual impairments who rely on screen readers. 

Alt Text Vs Descriptions 

Alt text is a short, concise descriptive phrase or sentence added to an image’s code conveying purpose or context and is only seen by those using screen readers. Alt text should be no longer than 120-140 characters (the size of a Tweet). Complex images may contain too much information to be effectively described using just alt text. For these situations, add a detailed description of these images in the surrounding text or in the notes section of a PowerPoint.

Focus for 2025-26 Academic Year   

  • Determine if the image is necessary for student understanding. If not, then remove the image or mark as decorative. 
  • Use the editing application or site’s alt text tool to add alternative text to all images. This is most often accomplished by right clicking (control click on a Mac) on the image and then selecting “add alt Text” from the pop-up menu.  
    • For Decorative Images: 
      • In Microsoft Suite applications (Word, PowerPoint), click on the check box to indicate the image is decorative. 
      • In Pressbooks, delete any irrelevant text auto populated and leave alt text blank (this marks it as decorative for this platform)
    • For Images where an interpretation is used for Assessment or in-class knowledge checks, write a short descriptive alt text saying, “XXX… used for assessment.” 
    • For Images with text on the page that already explains what is in the image, write a short descriptive alt text saying, “XXX…long description is in body of text.” 
    • For Images in PowerPoint with a description in the notes, write a short descriptive alt text saying, “XXX…long description in notes.” 
    • For all other Images: 
      • Think about the purpose of the image and what you want the students to learn from the image. 
      • Then, in as few words as possible (120-140 characters), describe the image. Focus on the key data and leave out extraneous visual elements. Aim for brevity and clarity. 
      • If your image cannot be described in this way, consider adding a short descriptive alt text and then describing it in the caption, the surrounding text (Word, Pressbooks) or in the notes (PowerPoint). 

Examples 

  • For this image on page 23 from the PPT “PHARM Antibiotics Part 2”, click on the image, then in the pop-up right hand menu click the box that is labeled “Mark as Decorative” because the image has no educational purpose. 
  • The alt text for this Image on page 5 from the PPT “Pathology of Valvular Disease” Could read, “Anatomical dissection of a human heart valve used for in-class knowledge check” because the image will be used to test student knowledge in class. 
  • The alt text for this Image on page 1 from the course pack “Spinal Cord and Spinal Nerves” could read “Anatomical divisions of the nervous system. Long description in the surrounding text and image caption” because the image is described in the surrounding text and in the caption. 
  • See the following slides for examples of alt text and long descriptions on PowerPoint slide decks: 

More Resources  

  • 01-07-26 BTT Half-Day Retreat Resources 

A More Detailed Why 

It’s crucial to add alt text (alternative text) to images and diagrams because it provides text descriptions for users with visual impairments who rely on screen readers, allowing them to understand visual content, and ensures content remains accessible when images fail to load due to slow internet or browser issues, making digital information equitable for everyone. Without it, screen readers just say “image,” leaving users with no context, while good alt text conveys the image’s meaning, function, and importance, just like a sighted person would understand it.  If the image is described in the surrounding text, alt text should indicate this (i.e. “chart described in surrounding text”).