W3 Accessibility Guidelines Core

Non-text Content

All non-text content that is presented to the user has a text alternative that serves the equivalent purpose

The intent of this Success Criterion is to make information conveyed by non-text content accessible through the use of a text alternative. Text alternatives are a primary way for making information accessible because they can be rendered through any sensory modality (for example, visual, auditory or tactile) to match the needs of the user.

W3 Accessibility Guidelines PDF

The objective of this technique is to provide text alternatives for images via an /Alt entry in the property list for a Tag. This is normally accomplished using a tool for authoring PDF.

PDF documents may be enhanced by providing alternative descriptions for images, formulas, and other items that do not translate naturally into text. In fact, such text alternatives are required for accessibility: alternate descriptions are human-readable text that can be vocalized by text-to-speech technology for the benefit of users with vision disabilities.

When an image contains words that are important to understanding the content, the text alternative should include those words. This will allow the alternative to accurately represent the image. Note that it does not necessarily describe the visual characteristics of the image itself but must convey the same meaning as the image.

Example

This example is shown with Adobe Acrobat Pro. There are other software tools that perform similar functions.

Choose Tools > Advanced Editing > TouchUp Object Tool
Access the context menu for the image and choose Properties.
On the TouchUp Properties dialog, select the Tag tab.
On the Tag panel, type the text alternative in the Alternate Text text box.