Alt text is critical for accessibility, as individuals using screen reader devices would not know what the image is about without a good description in the alt text. Some images, like infographics, are too complex to describe in detail within alt text. If an image is complex, how then do you maintain accessibility while giving the detail needed?
Length of Alt Text
Alt text has no official limit in length, however best practices encourage alt text of no more than 125 characters in length.
If an image cannot be described (within the context of the content) in 125 characters or less, it’s best to describe the image in other ways
Describing Complex Images
If your image is complex and requires a lengthy description it would also benefit your sighted students to view the description. There are several suggested actions for describing a complex image.
- If the content displayed in the image is already described in the text content of the page, it’s best to give the image an alt text containing an overview of the image plus a note about it being described in the content.
- For example, if a page contains an infographic about Gagne’s Nine Events of Instruction, but the non-graphical text of the page also details Gagne’s Nine Events of Instruction, then a good alt text for the infographic would be “Gagne’s Nine Events of Instruction, described in the content of this page”.
- If the content displayed in the image is not described in the text content of the page, it’s best to give the image an alt text containing an overview of the image plus a note about where a longer description is contained.
- A longer description can be contained in a separate location. There must be a link to the separate location to accompany the alt text. In this scenario, placing a link to a description directly below the image and titling it as “Description of image” would be effective. For example, an image can be described in a text document attached to the link.
- Consider having a textual description of the image available for everyone to read. Some complex images are tough to view for any person, and thus providing a description would be effective for everyone. Additionally, consider the necessity of the image if it is overly complex and difficult to read.
- A complex image that is purely decorative and imparts no added value or content can be described as decorative in its alt text.
- If the image is an image of words only, it is advisable to remove the image fully and replace it with standard textual words. If this is not done, the image must be handled like any other complex image and must have a corresponding description.
- If the image is of a mathematical or scientific notation, the image must be described. In many instances, consider utilizing tools that support MathML to create math and science notation that is fully accessible for all students.
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