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.
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>
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" />
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" longdesc="http://www.karensorensen.com/johnson-long-desc.html" width="400" height="290" />
Here's a video on how a screen reader reads a long descriptions.
- Guidelines for Describing STEM (Science Technology Engineering and Math) images
- How Do We Access Meaning in Art? (Describing art images in alt text)
- Effective Practices for Description of Science Content
- Open University's Guidelines for describing visual teaching materials
- UKAAF (UK Association for Accessible Formats ) Guidance
- Diagram Center's Accessible Image Sample Book
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 Distance Learning also can help you create tactile graphics for your courses. Please contact Haris Gunadi or Karen Sorensen 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.
Sounds can sometimes be used to differentiate variation in slope.
- MathTrax: a graphing tool that works with screen readers.
- IVEO: tactile graphics with audio description