Alternative text is a textual description of an image. It is used in web browsers in place of displaying an image. People with visual disabilities need assistance in understanding what message an image is trying to convey because they cannot see, or have difficulty seeing the image. In addition, some web browsers do not support images (i.e.: handheld devices).
For people with visual disabilities the Alternative Text is read by screen readers to describe an image. The purpose of Alternative Text is to provide an experience as close as possible to that of being able to actually see the image, even when the image is never actually "seen".
Types of Alternative Text
There are three basic types of Alternative Text:
1. Alt tag - an "Alt Tag" is a short description, usually 8-10 words, or less. The "Alt Tag" is embedded directly in the web page.
2. Long Description - a description that is usually longer than 8-10 words. It is accessed through a "d" link. A "d" link allows people to click on the small letter "d" next to the image to open up a new page containing the entire presentation.
3. Decorative Image - an image that is used purely for decoration and does not add or take away anything significant from the message of the page. An example would be a line which is used to visually separate two items on a screen , like a line separating the Title of a page from the content of a page. When an image is encoded as a a "Decorative Image" it is assigned a null tag which tells a screen reader to ignore it.