EPUB 3 Accessibility Guidelines

Although image formats can be used to create fixed layouts, doing so can greatly reduce the accessibility of the publication. When using images, keep the following guidelines in mind:

• Avoid empty files that set an image to render using the CSS background-image property. Not only does it leave the image without a description, but any reader without a CSS-aware reading system will see an empty document (note that even if the system does not handle fixed layout metadata, it will still render the publication). See the section on background images for more information.
• Avoid embedding text into images. Doing so removes access from assistive technologies. Use the CSS z-index property to define layering and position of text as needed on the image.
• Whenever possible, use figures and captions to add images to the fixed layout document (including the description in the caption). If you are using fixed layouts to facilitate the rendering of image galleries, plates and similar, you can use scipting to enahnce the default experience and remove the caption from visual display. The caption will be accessible to those who need and can also be presented generally in interesting ways (see the Samples section for an interesting implementation using this technique).
• Add a text serialization of the work if it is completely visual in nature. It's not true that readers who are blind or have low vision are not interested in reading these works, but fully representing the publication typically requires more than image descriptions.