Complex images contain substantial information – more than can be conveyed in a short phrase or sentence. These are typically:

• graphs and charts, including flow charts and organizational charts;

• diagrams and illustrations where the page text relies on the user being able to understand the image;

• maps showing locations or other information such as weather systems.

In these cases, a two-part text alternative is required. 

• The first part is the short description to identify the image and, where appropriate, indicate the location of the long description. 

• The second part is the long description – a textual representation of the essential information conveyed by the image. The examples shown in the video below illustrate different approaches that can be used to provide such short and long descriptions.

There are situations where the composition of an image is important and needs to be provided in the long description. For example, the sequence of colors used and the relative heights of the columns in a bar chart may be relevant information about the structure of the chart, in addition to the actual values and trends that it depicts.

Complex images can be difficult to understand by many people – especially those with low vision, learning disabilities, and limited subject-matter experience. Make long descriptions available to everyone to reach a wider audience with your content. For example, show the description as part of the main content. It may also be possible to reduce unnecessary complexity in your images and make them easier to understand for everyone.

It is also good practice to refer to and summarize more complex images from the accompanying text. For example, a reference such as “The following graph shows that visitors were lost in the first quarter, but the numbers recovered in the second quarter” helps to point out the relevant information that the image is intended to present.

If you’d like more information on alternate text and descriptions for complex images, see Arizona State University’s Accessible Images: Complex Image Guidelines.