Complex Images
“Complex images” is a broad umbrella term that covers a wide variety of dense visual information used for various purposes throughout STEM fields. It might be helpful to remember the purpose of digital accessibility features is ensuring equal access to and use of information.
Access
Access to the ideas and concepts your images are inteded to help illustrate
Use
Use of the data embedded in the images that is necessary for participation, engagement, and understanding
What Makes an Image Complex
An image is complex when it contains information that cannot be captured in a short phrase and becuase of that the text alternative needs to move out of the standard alternative text field.
Benefits of Leaving the alt Field
Part of the reason for moving out of the alt text field into the main content is to benefit from built-in functionality of other features like headings, lists, and tables. These special types of content allow improved navigation and control for assistive technology.
How to Create Alternative Formats
No single format meets the needs of all students. The best choice depends on the type of complex image and your learning objectives.
Text Descriptions
The most universally beneficial format. Good descriptions are:
- Concise—unnecessary words confuse learners
- Clear—use plain language appropriate to your audience
- Meaningful—focus on what matters for comprehension
Lists
Lists work well for showing relationships between elements—ideas, activities, categories, and their connections.
Image types that convert well to lists or tables:
- Pie charts
- Bar charts (horizontal and vertical)
- Line graphs
- Flowcharts and tree diagrams
- Circuits and schematics
- Free body diagrams
Data Tables
Tables work well when learners need to compare specific values.
alt text field, or otherwise clearly specify where to find the additional description and information. Use a heading and refer to it by name.Where Alternative Formats Go
Text alternatives can be placed in the document in several ways depending on size and type.
Caption
Include a visible caption near the image that describes its key content. Best for text descriptions. If comfortable with html, <figure> and <figcaption> are a model here, but semantic tags aren’t necessary if the intent is clear.
Surrounding Text
Describe the image in the paragraph immediately before or after it. Best for short lists and small tables. Give the image a name in the alt text to be able to refer to it in the page.
Link to Full Description
Provide a link to a separate section, slide or page with the complete description. Best for long tables that would have significant impacts on content organization. Make sure to label the section with a heading and refer to it in the alt text or nearby. Internal links can be convenient too.
When to Choose Which Format
flowchart TD
A[Complex Image] --> B{What's the purpose?}
B -->|Show relationships| C[Lists]
B -->|Compare values| D[Data Table]
B -->|Explain concept| E[Text Description]
B -->|Show process| F[Numbered List]
C --> G[Combine with brief description]
D --> G
E --> G
F --> G
accTitle: Choosing Alternative Formats
accDescr: A decision flowchart for selecting the appropriate alternative format. Complex images branch based on purpose: showing relationships leads to lists, comparing values leads to data tables, explaining concepts leads to text descriptions, and showing processes leads to numbered lists. All paths combine with a brief description.
The best approach often combines formats—a brief text description plus a table or list for detailed data.
Writing Effective Descriptions
Knowledge of your subject area helps you describe images meaningfully.
Questions to consider:
- What is the content and purpose of the image?
- What is the main focus?
- Is your audience novice or expert?
- Does the image contain text that must be included?
Guidelines for writing:
- Move from general to specific
- Use words rather than symbols for mathematical expressions
- Present information in logical order
- Separate detailed data from the overall description
- Focus on key information, not decorative elements
- Consider the 5Ws: Who, What, Where, When, and Why