Overview
Visual content can be informative or decorative. The same goes for audio and video content. Purely decorative content does not need alternative text – such content must be integrated so assistive technologies like screen readers can ignore it. The alternative text (also called “alt text”) of an informative image must offer equivalent content, so the same level of information is conveyed to the user. Therefore, in most cases, it is not so much the appearance of an image that needs to be described, but rather its purpose, function or the message it conveys.
Note: Further information is available at the W3C, in the “Understanding SC 1.1.1 – Non-Text Content
Who Benefits
Non-text content such as images, graphics and videos are not visible for the blind, or hardly perceivable for the visually impaired. Similarly, audio content is not perceivable to the deaf and hard to perceive for the hearing-impaired. Make sure such content comes with alternative text-based descriptions that can be reliably conveyed and interpreted by user agents and assistive technologies. As these issues are related to perception, people with sensory limitations will be the ones experiencing situations of disability if non-text content is not ultimately conveyed as text.
Reminders
Keep the following in mind when providing accessible solutions for this success criterion.
- Alternative Text (Active Images): All linked images must have a descriptive text alternative that serves the same purpose and presents the same information as the linked image.
- Alternative Text (Informative Images): Images that convey content must have a descriptive text alternative that serves the same purpose and presents the same information as the image.
- Alternative Text (Complex Images): Images that are too complex to be fully described in a short text alternative must have their purpose described using an extended text alternative.
- Alternative Text (Decorative Images): Images that do not convey content, are decorative, or with content that is already conveyed in text must not be given a text alternative that is exposed to assistive technology.
- Alternative Text (CSS Images): Images not normally exposed to assistive technology must either be pure decoration or have a text alternative.
- Alternative Text (Input Type Images): Form controls comprised of images must have a text alternative or an accessible name.
- Alternative Text (Captcha): Interactions designed to verify human users must not rely on a single sense to be successfully completed and alternate forms using different modalities must be provided to address the needs of people with different disabilities.
- Alternative Text (Audio or Video): Text alternatives must be provided to identify the purpose of the video or audio content.