Understanding Image Long Descriptions
The Web Content Accessibility Guidelines and Section 508 guidelines require you to include long descriptions for each image in an HTML document. You can use the longdesc attribute and a long descriptions stored in an external .txt file to assign a long description to an image. When you use this approach, the long descriptions are referenced in the HTML <img> tag in the longdesc attribute as shown in the following example:
<img src=“mission.gif” height=“240” width=“386” alt=“The Mission” longdesc=“mission.txt” />
The longdesc attribute in the <img> tag provides a link to a separate page where a long description is available. The link is invisible to sighted users, but when a conformant screen reader application reads the longdesc attribute, it loads the file referenced in the longdesc attribute and reads it. In the previous example, the screen reader would load and read the mission.txt file.
ePublisher provides the following options for assigning long descriptions to images:
You can use the ImageLongDescText marker to assign a long description to an image. With this method, you assign a long description to an image using a description you include in a marker you insert into your source document. For more information, see “Specifying Long Descriptions for Images in Word” on page 257.
You can use the ImageLongDescByRef marker to assign a long description to an image by referencing a long description saved in an external text (.txt) file. With this method, you specify the path to the external text file in a marker. For more information, see “Using Text in External Files to Assign Long Descriptions to Images in Word” on page 259.
If you assign long descriptions to some, but not all of you images, you can use the ImageLongDescNotReq marker. Use this marker when you use accessibility reports to verify that all images have long description but you have certain images in your source document that do not require a long description. For more information, see “Excluding Images from Accessibility Report Checks in Word” on page 262.
Although using the longdesc attribute is recommended in the Web Content Accessibility Guidelines and in 508 guidelines, older screen readers and many current browsers do not support this attribute and few online content developers use this attribute. As a result, the longdesc attributed benefits a only a small number of users. Only users who use modern screen readers can access the longdesc attribute easily. Older screen readers did not support this attribute. In addition, even users who use the latest version of screen reader may be unfamiliar with the longdesc attribute and may not know how to access long descriptions using their screen reader because the longdesc attribute is used so infrequently in online content.
If you use the ImageLongDescText marker to assign long descriptions to images, as an interim solution ePublisher allows you to display a D link immediately after the image. The D link is an upper case letter D link that directs users to another page that contains the text you specified in the ImageLongDescText marker. Although a D link is not required for accessible Web pages, it can be used in addition to the longdesc attribute. The D link technique works in all browsers, but it is less elegant than using the londesc attribute. Some users may be confused when they see a D link on the page, while other users will ignore the D link.
If you want to use D links in addition to the longdesc attribute when you generate output, your Stationery must have the D link option enabled. If you have permissions to modify target settings in ePublisher, you can enable the D link option setting in an project. For more information about enabling the D link option in an project, see “Specifying Accessibility Settings” on page 327. For more information about permissions required to modify target settings using ePublisher Express, see “Customizing Target Settings” on page 325.