Charts help readers better understand quantitative information, by illustrating the relationships among data or showing trends over time. Making charts accessible can help not only people with disabilities, but also non-visual learners.
Descriptive images need text equivalents in order to be accessible. Text equivalents (also called "alt text") are phrases or sentences that describe an image's visual appearance and provide any additional useful information. Depending on the audience and the author's motivation for using an image, the text equivalents may also describe what the reader is expected to learn from the image, instructions on how to take action (such as clicking an arrow image to navigate through online help), or how the image relates to the adjacent text.
Proper formatting, accomplished through heading markup, makes the document's navigational structure understandable to screen readers, refreshable Braille, and other assistive technologies (whereas merely using a larger or bolder font to indicate a section heading makes the document appear to be one long paragraph). Proper formatting makes the hierarchical relationships inherent in the content readily apparent to all readers, with or without disabilities.