No matter the type of image you are writing alt text for, you will want to keep a few overarching factors in mind.
Consider General Accessibility Concerns
Alt text is important for those with low or no vision. These individuals may have had visual impairment from birth or an early age, making them unfamiliar with what may be key descriptions for a sighted person.
Consider, for example, the use of color. Someone with no vision may not conceptualize different colors in the same way that someone with partial or full vision, or even someone who is colorblind, would. Therefore, it is important to avoid using color when unnecessary. For example, a line graph may use color to differentiate three different variables plotted on the graph. However, describing those lines by color would not be helpful. Rather than saying “the blue line trends upward,” say something like “the line representing females trends upward.”
You may also want to avoid placement descriptions, such as left and right.
A screen reader will read both the alt text and the caption. Therefore, you don’t want to repeat information already provided in the caption. For example, let’s say a book includes a reprint of a painting. If the caption already identifies the artist, painting title, and a description, then your alt text may be as simple as “a painting.”
Consider the Length
Some typesetting programs may have maximum word counts for alt text. At Cognella, we currently do not have a word limit for long alt text.
Even though no word limit exists, simply consider the time it will take a student to listen to and absorb the alt text. Keep your purpose in mind and limit yourself to only the necessary information to provide a fair learning experience.
Consider if Alt Text Is Needed at All
There may be times you determine that you don’t need to provide alt text for an image. If it’s not needed, be sure to indicate it by noting “null” in the spreadsheet column for “Short Description.”
A few scenarios where an image may not need alt text are:
- The image is used for design purposes only. For example, an icon added to the margin each time the heading “Consider This!” appears.
- The image is an uncaptioned stock photo. In these cases, you can simplify your description, or you can simply choose to use “null,” since aesthetic images are not crucial to student understanding.
For More Information
Alt text decisions: https://www.w3.org/WAI/tutorials/images/decision-tree/
Alt text writing: https://webaim.org/techniques/alttext/
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