As you saw in Game Changing Technology [YouTube Video], many people rely on screen reader software to access content, including users who are blind or have low vision. Adding alt text and long image descriptions when needed ensures everyone can access visual information. This strategy aligns with Multiple Means of Representation, a foundational principle of Universal Design for Learning. In our textbooks, every image also has a figure caption. The content in the figure caption will help you determine what should go in the alt text or long description. Let’s discuss how these three parts – figure captions, alt text, and image descriptions – work together.

Key Definitions

Figure Captions are one to two sentences of textual description that contextualize the image content within the surrounding text. Every image in your textbook includes a figure number as well as a figure caption. Figure captions often pose a question, draw a contrast, or explain an illustration. The caption is readable to all textbook users with or without screen reader software.

Alt text, or alternative text, is the short text substitute for visual information conveyed by an image, chart, or graph. Alt text can also be called an “alt tag.” Typically, alt text is only read by users who use screen reader software. It isn’t visible on the page. Alt text is not necessarily a literal description of the image. Instead, alt text aims to capture any visual information that relates to the purpose of the image.

Image descriptions include rich detail and are longer than alt text. Image descriptions convey numbers, trends, and patterns that alt text and figure captions usually won’t describe. Image descriptions accompany alt text when more than 10 words are necessary to communicate the relevant visual information. This is often the case for infographics, charts, and graphs. In these cases, the alt text can also include the phrase “Image Description Available.” Image descriptions are intended for users who need more detail about the visual information of an image. Often these users will include people who may not use screen reader software but who benefit from more orientation to visual information. In our project, image descriptions will be linked next to an image, which will bring users to the bottom of the Pressbook page. All users will be able to access them. Image descriptions will be included in print versions as well.

Key Examples

Sometimes the figure caption will convey all relevant detail about the visual information in the image already. If this is the case, adding alt text is redundant. Adding alt text is only necessary when the visual information conveyed by an image is not otherwise available to users who use screen reader software. Here is an example of when alt text is not necessary because the figure caption is quite detailed:

Most of the time, however, the figure caption won’t summarize the visual information of an image in detail and alt text will be necessary. Here’s an example:

In the above figure caption, the visual information of the image is not described in the caption itself; the image supplements the text. In order to convey the visual information, the alt text reads: “An unzipped glucometer kit and accessories.”

Please note: Sometimes alt text will include information that is relevant to all users but only appears in alt text. In these cases, the information should be moved to the figure caption instead. For example, let’s say that the alt text for the above image listed each accessory, but the list wasn’t available in the surrounding text or figure caption. This would mean that the alt text had relevant information but didn’t share it with all users. The list of accessories would need to be included in the surrounding text or figure caption.

What do I do if there is no alt text or image description for an image?

To determine if you need to add alt text or an image description, start by considering purpose of an image. Some images are informative in that they convey important content. This means they are considered meaningful to the argument, guiding question, or message of a work. Other images only break up the visual flow of a page or just add visual interest. These images are considered decorative. If an image is decorative, it requires no alt text. Most images in this project will be informative and will require alt text and/or image descriptions when the figure caption doesn’t already convey key visual information.

Self-comprehension Check

Select the four hot spot icons below to learn more about the parts of a figure, including figure number, figure caption, image description, and alt text.