Accessible Images
It is important to ensure that images in instructional materials, slides, and course websites have appropriate text alternatives (alt text) and/or descriptive captions. These practices support all learners, including those using screen readers, to access important visual information.
What is ALT text?
Alternative text, also known as alt text, is descriptive text that conveys the meaning of an image in digital content. Without alt text, people who use screen readers cannot access the content provided in the images. Alt text is a requirement in the Section 508 guidelines for creating digital content.
What are captions for images?
Captions for images are text descriptions of an image that are displayed on a course or webpage. It provides supplemental information for both sighted and non-sighted users about what the image is conveying. Image captioning is recommended by the Universal Design for Learning (UDL) principles when there is a need to further explain the purpose and information about an image.
GSA Section508.gov (3:25)
Microsoft 365 (3:41)
Best Practice Guidelines for Accessible Image
1. Focus on Key Elements and Describe Meaning, Not Just Appearance
Describe the essential details and the image’s significance rather than its visual elements.
2. Be Concise but Descriptive
Alt text should clearly and correctly represent the image’s content and function. Avoid excessive details that burden assistive technology users. Keep alt text brief (typically 8 to 80 characters, under 125 if needed). Use a longer description if the image is complex.
3. Use Keywords Thoughtfully and Avoid Redundancy
Prioritize clarity and include relevant keywords naturally, especially in academic or professional settings. Do not restate details already provided in the surrounding text.
4. Do Not Use Phrases like "Image of" or "Graphic of"
Assistive technologies already announce images, so these phrases add unnecessary redundancy.
5. Consider Context
Tailor descriptions based on surrounding content to avoid redundancy. Provide only missing or necessary details.
6. Mark Decorative Images Properly
Use alt=”” for decorative images that do not convey additional information.
7. Describe Linked Images
If the image is a link, explain the image and also the function or destination. If an image is a button or icon, describe its function (e.g., “Search icon” or “Download report”).
8. Handle Complex Images with Extended Descriptions
Use short alt text for quick reference and provide a longer description elsewhere when needed.
9. Identifying the Type of Image
If relevant, specify whether an image is a logo, illustration, painting, or cartoon. This helps provide context, especially for non-decorative images.
10. Providing Additional Descriptions for Data or Diagrams
While “Handle Complex Images with Extended Descriptions” covers this in general, it might help to explicitly mention that charts, graphs, or diagrams should summarize key takeaways rather than just describing the appearance.
Tips for Different Disciplines
- Science & Data: Focus on trends, key results, and significance.
- Humanities & Art: Describe historical context, composition, and symbolism.
- Social Media & News: Prioritize clarity and engagement while avoiding clickbait.
Self-Evaluation Questions
Use these questions to assess whether your document meets accessibility standards:
- Does the alt text describe what is in the image?
- Is the alt text too simple and/or too generic?
- Is the alt text within 8 to 80 characters long?
- Does the alt text provide repetitious information?
- Is the image meaningful? Should it have alt text or should it be null (Alt=””)
Additional Resources
- Authoring Meaningful Alternative Text, GSA Section508.gov
- Write helpful Alt Text to describe images, Digital Accessibility, Harvard University
- Add an Alt text to an image, Universal Design Center, CSU Northridge
- Descriptive Text for Images, Universal Design Center, CSU Northridge
- Web Accessibility Criteria, Universal Design Center, CSU Northridge