Accessibility practices and tools: Alt text
Describe images that convey information.
Alternative text (alt text) helps students who use screen readers understand the content and purpose of images. It’s a key accessibility requirement and a simple way to make your materials more inclusive.
Why it matters
- Alt text is read aloud by screen readers, enabling blind or low vision students to understand visual content.
- Students with cognitive or learning disabilities also benefit from brief image descriptions that reinforce meaning.
What to do
DO add alt text that describes the image
EXAMPLE:
alt=”Scientific method: observation, question, hypothesis, experiment, analysis, conclusion”
AVOID adding alt text that is vague
EXAMPLE:
alt=”Blue diagram with six words”
- Keep alt text brief—ideally under 150 characters.
- Avoid phrases like “Image of…” or “Picture of…” as screen readers already indicate that it’s an image.
- Focus on the purpose of the image, not just what it looks like.
- For complex images (like charts or diagrams), provide a brief alt text and describe the details elsewhere on the page or in a linked resource.
- If the image is decorative—such as a logo, border, or icon used only for visual effect—mark it as decorative so screen readers skip it.
Getting it right
In Canvas
In UDOIT Advantage
UDOIT issue identified: “Alternative text should not be the image filename”
- Click the ‘Review’ button for more information.
- Enter a short description for your image.
- If the image is purely decorative, check the box labelled ‘Mark image as decorative’ and click ‘Save’.
UDOIT issue identified “Image elements should have an “alt” attribute”
- Click the Review button for more information.
- Add new alt text to the text field and click ‘Save’.
UDOIT issue identified: “Alt text for images within links should not be empty”
Hyperlinked images should contain alt text.
- As above, click the Review button for more information.
- Add the new alt text into the text field and click ‘Save’.
UDOIT issue identified: “Decorative images should have empty alternative text”
If an image is just for decoration, it should not have an alt text description.
- Click the Review button for more information.
- If the image is purely decorative, uncheck the box labelled ‘Mark image as decorative’.
- Delete the alt text.
- Recheck the ‘Mark image as decorative’ box and click ‘Save’.
In Microsoft Word or PowerPoint
Right-click the image, choose “Edit Alt Text”, and add a description or tick “Mark as decorative”.
View more detailed support for adding alternative text in Word or PowerPoint.
In Adobe Acrobat Pro (PDFs)
Use the “Set Alternate Text” tool in the accessibility tags pane to apply alt text.
Related Canvas Baseline Practices and Universal Design for Learning
- Canvas Baseline Practices require all images to have alt text or be marked decorative.
- Universal Design for Learning encourages providing content in multiple formats so all students can access and engage with learning materials.
Tools and checks
- UDOIT (Canvas) – scans for missing or unclear alt text.
- Canvas Accessibility Checker – highlights images without alt text or improperly marked decorative images.
- Microsoft Accessibility Checker – identifies missing or placeholder alt text in Word and PowerPoint.
Page updated 21/07/2025 (content refresh)