Long Description

Long descriptions provide a textual version of the essential information conveyed in a detailed or complex image.

You may already be familiar with simple alternative text, which provides brief descriptions of visual content. But, when an image is detailed and complex, simple alternative text isn’t sufficient enough to capture its meaning.

Complex Images

If an image can't be described in 120 characters or 1-2 sentences, it is probably a complex image. Some common examples of complex images include:

Charts
Graphs
Infographics
Cartoons
Smart Art
Flowcharts
Maps
Illustrations

The Two-Part Approach to Complex Images

Even though your long description provides the actual description of the image, you still need to alert screen readers to the image. You also need to ensure that users can make the connections between the image in the original location and the long description. To do this, a two-part text approach is needed. The first part will include a brief snippet of alt-text, identifying the image and (when necessary) the location of the long description. The second part will consist of the long description.

Check out the example below that shows how to make the connection:

Alt Text: “Chart 1.2: Long Description is located in Appendix A."
Long Description: “Chart 1.2 suggests that…” (in Appendix A)

Make Complex Images Accessible

To make a complex image accessible, you should:

Use a static, flattened image: do not embed graphs or interactive charts in your document, as these often exist on separate drawing layers that are not accessible to screen reader users. Instead, take a screenshot of the chart or graph, and use that image. The image should be a single, non-interactive object.
Add a descriptive caption: include an image ID and a brief explanation of what the image shows (e.g., Figure 1: Map of Greece or Table 3: Revenue Growth in Quarter 3).
Provide alternative text: this text should be short and formulaic. Reference the image ID, and direct users to where the long description can be found (e.g., Figure 1. See below for detailed description).
Provide a detailed long description: this should convey all meaningful content and relationships shown in an image.

Long Description

Formats

Some options to support complex image accessibility include:

Paragraph(s) of text: these should ideally be positioned close to the image (either above or below the image in a Word document OR on the same slide or next slide in a PowerPoint presentation)
A simple table: sometimes, slightly more complex bar or pie chart data can be presented in a simple table format
A list of data points: sometimes, slightly more complex bar or pie chart data can be presented in a list format
Video content: if you have described the image in full detail in a lecture video – and please note that you must describe the image in full – you can indicate the title of the video and exact timestamp where the description begins
Appendices, Notes, or external websites: You can link to any of these that are appropriate and that your audience will have access to in the body of your text – just remember, you can’t add links to alt-text

Location

Because long description is rather lengthy and detailed, it can’t be put into alt text fields. Instead, you’ll need to decide where to put it. You have several options:

In the surrounding text or slides
In an appendix or appendix slide
In the speaker notes (PPT)
In an attached video
On an external site that has been linked

Tips for Writing Long Description

Identify the type of image in the first sentence. Knowing what type of image (cartoon, bar graph, pie chart, diagram, illustration) is being described is essential for comprehension.
Summarize the point of the image in your second sentence. Identifying the overall point of the information being presented provides important context and direction.
Use spatial references. What is on the right side of the image? In the top corner? Left side of the image? Lower bottom quadrant?
Use x- and y-axis. If you are working with a chart or a graph that uses a x- and y-axis, identify what each axis measures.