Complex Images

If you have complex images in your document, such as bar charts, organizational charts, electrical diagrams, maps, infographics, etc., you will need to provide lengthy descriptions of them to make them useful to blind users. You could add all the text as alt text, but that’s not ideal. Alt-text is meant to be relatively brief. There is no official limit on the allowable length of alt text, but a maximum of about 150 characters is often cited as the best practice limit.

The reason that alt text should be brief is because screen readers treat alt text as one big chunk of text, and they don’t allow users to interact with the alt text. They cannot pause the screen reader within the alt text, to go back and read the previous word for example like they can do within normal text. In fact, if the user pauses in the middle of lengthy alt text, they can’t even pick up where they left off. They have to start over at the beginning of the alt text. The longer the alt text is, the more frustrating that is for the user. If the text were in the regular flow of the document, users would be able to interact with it, pause, rewind, pick up where they left off, hear the characters letter by letter, and navigate the text in other ways, but alt text is different, and doesn’t allow that kind of user interaction. Another weakness is that alt text does not allow any formatting. You can’t separate it into distinct paragraphs, or add lists, or tables, or anything else. It is just text.

Option 1: Add a Long Description to the Document Itself

One of the easiest ways to provide a long description for a complex graphic is to write the description in the text of the document itself. There is no character limit when you do that. In fact, you can even add bulleted lists, tables, and any other kind of formatting that may be useful. You could provide the description before or after the image; whichever makes more sense. Providing this information within the visual text makes the image more accessible to all users rather than just those who use a screen reader.

Option 2: Add a Link to a Footnote or Endnote

If the long description would interrupt the flow of the document too much, you can provide a hyperlink to a footnote or endnote with the long description. The description is still available in the document, and still easily available to screen reader users, while still preserving the original flow of the document.

Option 3: Add a Link to an External Resources

In some cases, it may be more appropriate to add a link to an external resource, such as a web site, which contains the long description. This is less convenient for the reader because it requires exiting the document and opening a web browser. It’s also riskier in some ways, because you may forget about the web document and delete it or move it, making it unavailable to people. But this is still a legitimate strategy if none of the other options is possible.