Provide a full text description for content images

Generally, the best that alt-text can do for content images is provide a brief description of the format and subject of an image. To fully describe the information contained in an image to a nonvisual user, we need to use other methods.

HTML allows for a full description of image content by providing the LONGDESC attribute of the IMG tag. The content of LONGDESC is a file address pointing to a file that contains a text description of the image. When a nonvisual user encounters an image with a linked text description, he or she loads the linked file, reads the description, and then returns to the originating page.

Another way to provide a full image description is to provide image captions. This approach benefits both visual and nonvisual users because text may prove helpful in comprehending the image. For example, an image caption explaining the contents of a graph or chart allows nonvisual users to access the information via the caption, and helps visual users to better their understanding (Figure 4.8).

Figure 4.8: NASA screenshot

Figure 4.8: NASA includes captions (1, 2) for the images on its site. The captions provide information about images for both visual and nonvisual users.