Accessible Images in Course Content

The core WCAG requirement is that information conveyed by non-text content is available through a text alternative. The World Wide Web Consortium (W3C) Images Tutorial and its alt decision tree are widely used references for deciding what alt text to provide (informative vs decorative vs complex).

Common pitfalls

  • Alt text that repeats “image of…” without meaning. Screen readers announce images automatically, so this information is repetitive.
  • No alternative for text-heavy images (flyers, screenshots, scanned pages)  
  • Charts with no text summary or data alternative  

Alt text examples for images

  • Photo used only for decoration: "decorative"
  • Photo used for instruction: “Professor demonstrating proper pipette angle (tip held at ~20°) before dispensing into microtube.”  
  • Chart: “Bar chart comparing test scores for sections A and B; Section B’s mean is higher by ~8 points.” Then provide the underlying data in a nearby text/table. (Complex images typically need a short alt plus a longer description or data table.)  

NOTE: If the image supports learning, include what it is, what matters for the learning objective, and (if needed) the key data shown.