Alt Text for Complex Images

Describing complex visual content, such as flowcharts and diagrams, can be difficult.

When using complex visuals, ensure all users:

• Are aware there is an image with information
• Understand the nature and purpose of the image
• Are informed that the image is complex
• Know how and where to get more information (if appropriate) ^[1]

On this page:

• Complex Visuals
• Beyond Alt Text
• Complex Visual Workflow
• Further Reading

Beyond Alt Text

As mentioned in the prior chapter, alt text should be brief. For a complex image, it may not be feasible to describe the image in 1 or 2 sentences. Additionally, alt text does not support lists and headings. Structured text is essential to make long text digestible for screenreader users. That is one of the reasons why alt text should be brief.

Additionally, alt text cannot contain links. Links could be used to direct screenreader users to additional information about an image. However, links can be placed in figure captions.

When alt text may not be sufficient, consider:

Figure captions

• Figure captions are a label or description written under or beside a visual (such as the example image at the top of this page).
• Figure captions will benefit all users by clearly identifying the image, its purpose, and its relation to the rest of the material.
• Figure captions can include links to more information or who to contact for more information.

Text alternative

• For especially long descriptions, a text equivalent is recommended. For example, express a flowchart in text with headings and/or lists.
• Considering adding text adjacent to the image. Using text and images together is an effective method to reinforce important information and emphasize key points. If an equivalent description is available in adjacent text there is no need for alt text.
• If adding a text description adjacent to the image is not feasible, provide the long description at the bottom of the page or in an appendix. Make reference to the location of the description in the alt text or provide a link to the description in the figure caption.

Equivalent Data

For visual data, such as a chart, include type, relevant labels, and a brief summary.

• Include and link to or reference a table of the data used to generate the data visualization.
• Use the alt text to make reference to the available table data, such as alt=”See table 3 for chart data.”
• Use a figure caption to reference and link to equivalent data.
• Express image information using headings and lists where appropriate.

A best educational practice is to use images to reinforce information. Try to present information in text and add images to supplement and highlight key points and processes. By doing that, you may not need to describe complex images as the information is already provided in text format.

Complex Alt Text Formula

While the [Type] + [Focus] + [Details] alt text formula from the previous chapter is an excellent starting point, it may not be suitable for complex images. The World Wide Consortium has developed an expanded version:

“[Image type] illustrating [data type] showing [reason for including image]. This is a complex image and may require specific support for visually impaired students – please contact [Name of designated person] if required.”

As an example, consider this model of the global carbon cycle:

​To completely describe the information in this image would be impossible within the constraints of alt text. However, applying the complex image formula may be helpful:

“[3D landscape model] illustrating [global carbon stores (Petagrams) and fluxes (Petagrams/year)] showing [the complexity of the cycle and the main impacts of human interference]. This is a complex image and may require specific support for visually impaired students – please contact [Luke McKnight] if required”.​ (Note: remove [ ] before including complex image formula as alt text).

Complex Visual Workflow:

Adapted from Complex images – making sense for accessibility. Use the following prompts to determine the best way to provide a text alternative to complex images:

Can the essential information be described in a few brief sentences?

1. If yes, type a description of the image using the [type] + [focus] + [details] outlined in the previous chapter.
2. If no, ask:

Does nearby text include the information in the image?

1. If yes, mark the image as decorative or use alt text to direct users to text description.
2. If no, consider:

Is the information in the image available in other resources?

1. If yes, use figure caption to link to resource.
2. If no, consider using AI to generate an effective description.
   1. Use Ian Linkletter’s Alt Text Assistant to create descriptive text.
   2. Or, use CoPilot to generate a description. Consider asking CoPilot to “outline the information in the image” or “describe the image in detail.”
   3. Google Gemini can also describe images and may be useful.
   4. AI generated descriptions are improving, but must be verified for accuracy. Read the AI Generated Alt Text chapter in this guide for more information.

If the description (AI assisted or not) is more than a few sentences, format the output with paragraphs, headings, and lists. Include the long description in adjacent text or an appendix. Make reference to the long description in the alt text or include a link in the figure caption.

If no useful description can be created and/or it is not feasible to link to additional information, use the complex alt text formula explained above to direct readers to a support contact for further details.