Images are used to enhance visual presentation of the page. When used as a graphic representations of information, they can effectively illustrate concepts and convey ideas.
Text-equivalents for images let users of non-graphical browsers or assistive technology understand the information being conveyed by the image. If they are not present the screen readers vocalizes the name of the image file or other irrelevant textual information. Text-equivalents should not be used to describe the image but to convey the relevant concept or information represented within the graphic.
When using LONGDESC or D-Link , be sure to provide a way for the user to return to the page at the position of the image. Example for D-Link
Beside screen readers text descriptors are also used by search engines and devices such as mobile phones and PDA
Screen read all text, thus these technologies cannot ignore an image. It is important to provide meaningful description to the images and to assign 'null" value to alt attribute for redundant meaningless images used for spacers and other visual effects.
Image Types and Text Descriptors
| Image Type | Description | Text-Equivalent |
|---|---|---|
| Composition images-(slice) | Two or more images grouped to create a single visual composition | Alt =" text-equivalent for main image" and alt="" (null) for the remaining images |
| Graphic elements | Images used for visual presentation / "spacers" which convey no meaning | Alt ="" (null) |
| Repeated Images (symbols, directions, check marks) | Image repeated two or more times on a page | Alt ="same value" for every use of that image on the page |
| Bullets | Image repeated on page for bullets in lists etc. | Alt ="" (null) |
| Navigation Elements (link images) | Buttons, banners, or any images associated with a link. | Alt ="skip to content "; "go"; "NC State Logo" ; "Home" or the effect of following the link |
| Generic images (convey some information) | Photographs, images and graphics | Meaningful description Alt="name of person"; "Special Coverage" |
| Generic images (requiring richer descriptions) | Figures, illustrations, graphs, maps, symbols, graphics illustrating concepts | Alt="name"; and Longdesc="xx.html" or D-Link - <a href ..xx.html />link to external file |
| Thumbnail | Image that points to a larger image | Alt="description of the larger image" |
