Complex Image Accessibility

Most images can be made accessible using using alternative (alt) text descriptions. But more complex images require more description then the limited one or two brief sentences that may be used in the image alternative text attribute.

Text-based Description

Listed below are techniques on how to provide additional description to complex images (including graphs, maps, diagrams and charts.) They are recommended by the Diagram Center, a leading source on image accessibility.

Use a caption

For Web Pages: Your caption must be associated with the image, so make sure to properly add a caption using the ‘figcaption’ html tag. (Requires HTML editing.) Example code: <figure> <img src="johnson-birthplace.jpg" alt="" width="400" height="290" /> <figcaption> <em>Karen at President Lyndon B. Johnson’s reconstructed birthplace <br /> in Stonewall, TX</em> </figcaption> </figure>

Video on how a screen reader reads a caption.

For MS Word and PowerPoint: Right clicking on the image and select Add Caption.

Describe the image in surrounding text

If it is adequately described in surrounding text (including text-based tables), just add a short alt text label or description, so it’s clear what the image is and the student can correlate the image with the description.

With HTML based images, you can provide further clarification by using the aria-describedby property to tie that description to the image. (Requires HTML editing.) Example code: <img
src="johnson-birthplace.jpg" width="400" height="290" alt="Karen at
President Lyndon B. Johnson’s birthplace"
aria-describedby="johnson-birthplace" />

See this example of a screen reader reading the surrounding text and how to use the aria-describedby property.

Link out to a web page with a longer description

If the image cannot be adequately described in one or two brief sentences of alt. text, and it cannot be described sufficiently in the surrounding text, use the ‘longdesc’ attribute. Requires HTML editing. Example code: <img src="johnson-birthplace.jpg" alt="Karen at President
Lyndon B. Johnson’s reconstructed birthplace in Stonewall, TX"
width="400" height="290" />

Here’s a video on how a screen reader reads a long descriptions.

Description Resources

Tactile Representations

Sometimes touching a model or a tactile graphic is the best way to describe something.

Tactile graphics
Tactile graphics have different sized raised dots to show variation in graphs, charts and maps. The American Publishing House for the Blind has a tactile image library where you can purchase tactile images. Disability Services and Online Learning also can help you create tactile graphics for your courses. Please contact Haris Gunadi [opens in new window] or [opens in new window] for more information. (Guidelines for the creation of tactile images.)
Indicate if a model is available
If you know where a 3D model of the image is available, indicate that in your image caption or on the same page as the image.

Audible Representations

Sounds can sometimes be used to differentiate variation in slope.

Additional Resources