Not all EPUBs have images, but when they do, including alternative text for every image is essential to maintaining accessibility for all readers. Alternative text, or alt text, is different from including a caption for an image in your book; it is a clear description of what is taking place in the image so that readers who use voice-to-text software can understand its context. Used commonly on websites, alt text can be easily built into your InDesign document for all of your images before you convert your book into an EPUB—and here is how to write it.
Remember accessibility as you write.
The core purpose of including alt text is to assist readers with visual impairments or disabilities. Think of this reader as you look at the image and write the alt text. How would you describe this image to someone who couldn’t see it? What information is important?
What is your caption missing?
Your EPUB images may or may not include captions, but if they do, voice-to-text software will be able to read it along with the alt text. This means that your alt text should not be a regurgitation of the information held within the caption; instead, think of what is missing.
Is the caption explaining the context of the image so well that alt text isn’t needed? If not, what is the caption not doing that your alt text could?
Use brevity (with exceptions).
Since voice-to-text software will read both the alt text and caption aloud, keep your alt text succinct whenever possible. Make every word in your alt text pull descriptive weight, and try to keep your copy between one and three sentences long.
Of course, there are times when alt text must include transcriptions, like when there is text embedded within an image. In the case of important diagrams or figures that include text within an image—where the information is not explained within the surrounding text and is necessary for the reader’s understanding—then a full transcription should be included in the alt text. This is a case where the caption would act as a visual aide, while the alt text would provide longer, more descriptive information.
Paint a visual story with accuracy.
Providing an accurate, objective description of your images using alt text is important for establishing context for your reader. Determine what is taking place in the image and its context within the EPUB; or to put it simply: who, what, where, when, and why?
Concrete details and specificity are key, especially for nonfiction titles. However, that doesn’t mean imagery should be left completely behind within your alt text. Consider how you can work in descriptive language that paints a clear visual for your reader.
When proofing your alt text copy, ask a friend or colleague to close their eyes while you read the text aloud. Then ask these questions: Does it add context for the reader and provide essential information? Does your alt text take too long to read, or is it a proper length? Lastly, does it paint an accurate picture in the mind of your reader?
To practice creating and writing alt text for future titles, take advantage of online resources such as the Poet Training Tool. An initiative provided by the U.S. Department of Education, this interactive website has modules that help you understand when and how to describe images, as well as exercises for you to practice describing images provided to you.
Alt text is one way to keep your ebooks and EPUBs accessible, but knowing how to write alt text is only a small part of accessibility. Stay up to date with accessibility standards from the IDPF and take advantage of these user-friendly guides and resources provided by Inclusive Publishing.