Types of informative images include:
- Pictures and other bitmapped graphics
- Charts, examples include:
o Bar Charts
o Pie Charts
o Organizational Charts
o Flow charts
- Scatter plots
- Mathematical Equations
The type of text equivalent needed for an informative image depends on the purpose and information the image represents. For example, a news photograph of a public official is probably just highlighting or drawing attention to an article or story associated with the official, and a simple alt text can be used to fully describe the purpose of the image. A bar chart, on the other hand, conveys numerical information; the proper text description of a bar chart is a tabular data table, probably with some additional summary information, so that speech reader users can access the numerical relationships and trends visually represented in the chart. In cases of mathematical equations, text equivalents should be available as MathML.
Text equivalents for informative images that contain additional information should be integrated into the visual rendering of the web resources so that the information is available to all users. Since everyone has a unique style of learning, making the more detailed text equivalent available to all users often yields better understanding of the content in general.
Benefits to People with Disabilities
- Screen reader users can understand the purpose and content of informative images.
Benefits to Everyone
- Users navigating web resources with cell phone, PDA devices or text-only browsers can understand the image before it is downloaded or if the technology does not render the image.
altattributes help users identify images on your website.
Benefits to Developers
- The ranking of web resources improves as search engines can better identify images that are relevant to the search topic when
altattributes are meaningful.
- W3C WCAG 1.0 Image techniques
- Cynthia Says (HiSoftware AccVerify/AccMonitor) Alt Text Quality Checks
- WebAIM alt text quality checks
- ATRC Web Accessibility Checker
- 17: Images in HTML (Opera Web Standards Curriculum)
altattribute on an
areaelement should describe the target of the link associated with the link
altattribute should provide a short description of the purpose and information contained in an image
Related Accessibility Requirements
- § 1194.22.a A text equivalent for every non-text element shall be provided (e.g., via "alt", "longdesc", or in element content).
Illinois Information Technology Accessibility Standards
Web Content Accessibility Guidelines (WCAG) 2.0
Web Content Accessibility Guidelines (WCAG) 1.0
- 1.1 Provide a text equivalent for every non-text element (e.g., via "alt", "longdesc", or in element content). This includes: images, graphical representations of text (including symbols), image map regions, animations (e.g., animated GIFs), applets and programmatic objects, ascii art, frames, scripts, images used as list bullets, spacers, graphical buttons, sounds (played with or without user interaction), stand-alone audio files, audio tracks of video, and video.