Alt text, or alternative text, is a short description of an image that is linked to the image element in ebooks and makes the image more accessible for a variety of situations that rely on text to describe a figure’s content and function, such as for screen readers, search engines, and readers with low vision or cognitive impairments. Alt text is meant to be read aloud by technology and should be written with this in mind.
What Needs Alt Text
- All images unless they are purely decorative images.
- Alt text is not supported for tables at this time.
Writing Alt Text
Content
- Do not repeat or rephrase the caption.
- Keep the description brief—no more than 150 characters, including spaces and punctuation.
- Focus on information important to the reader and leave out irrelevant details.
- Use keywords and include only essential information. It is not necessary to include “photograph of,” “image of,” or similar wording.
- Include any text depicted in the figure if space permits.
Format
- Remove HTML/SML control characters (<, >, &, “, ‘).
- Delete or replace dashes with words (e.g., “23–28” should be written as “23 through 28” or “23 thru 28” to save space).
- Spell out uncommon symbols. Common symbols—for example, º, %—are acceptable.
- Limit use of punctuation, which may not be interpreted as intended (e.g., slashes, colons, ellipses, and parentheses).
- Avoid acronyms when possible although sometimes an acronym can be used effectively by adding hyphens between the letters.
- Spell out units of measurement (e.g., “km” should be “kilometers”; prime and double prime characters should be spelled out as “feet” and “inches,” respectively) but some abbreviations will work (e.g., “thru”).
- Numbers may need to be spelled out.
Testing Alt Text
- Check that your character count does not exceed 150 characters. Note that some figures will require a longer description but, if possible, include that information in the text or caption.
- Listen to the alt text using read-aloud technology to check for issues.
Examples of Alt Text
Alt text with no context:
Denver skyline with Longs Peak in the background
Alt text in a book about winter sports:
Denver skyline with Longs Peak prominently visible in the background, showing Denver’s proximity to the Rocky Mountains
Alt text in a book about air quality:
Denver skyline with Longs Peak in background, seen through a haze of pollution
Alt text with no context:
Five pot sherds with scale measured in centimeters
Alt text in a book about archaeology in Louisiana:
Five examples of Early Woodland period Tchefuncte pottery sherds from Midden A
Alt text in a book about the Tchefuncte potters:
Five examples of Tchefuncte pottery sherds that show decorative patterns and laminations and measuring between 2 and 9 centimeters
Alt text with no context:
Solo hiker walking on a mountain trail in Bavaria
Alt text in a book about geography:
The area around the Hochgrat in Bavaria, which depicts panoramic views at the top of a mountain trail as part of the Allgau Alps
Alt text in a book about mental health:
[no alt text needed because figure is purely decorative]
Alt text:
Bar graph of the average monthly snowfall at Alta Guard for the months November through April
Note:
Specific information from the graph must be described in the caption or the text.
