Issue
Complex images that contain information/data that can be difficult to describe, but without text alternatives the data is hidden from some users. Complex images include embedded images of data visualizations, such as:
- Maps
- Charts of all types (bar chart, line graph, etc.)
- Diagrams
What to do
Complex images require a two-part text alternative. This includes a short description (alt text) and a long description to provide a more in-depth description and access to the raw data.
- Short Description (alt text)
- Use the following formula:
“[Chart type] of [type of data] where [reason for including chart]”
- Use the following formula:
- Long Description
- Provides detailed information about visual content, including scales, values, relationships, and trends.
- Aims to convey the intended message of the data and helps users understand categories, trends, and extreme values.
- Artificial Intelligence (AI) tools can help you get started, but a AI-generated description MUST be verified and often edited by a human who knows the data.
- The most accessible way to provide this information is by publishing it as html and linking to it. Be sure to include a link back to your original content, though.
Recommended tools
- Canvas module: Images & Media: Web Content Accessibility (Digital Accessibility Basic Training Canvas course)
- AI tools (non-secured, use at own risk):
- Complex Images – Web Accessibility Initiative (WAI) covers different approaches on providing long descriptions.
- The Diagram Center has a pretty comprehensive set of guidelines for charts and graphs.
Who’s affected
People who:
- Use screen readers (blind, low vision)
- Have slow or weak internet (alt text is what shows up on the screen if the image is slow to load)