Provide text alternatives for non-accessible elements

Requirement: Every image, movie, sound or other non-text item should have some text description explaining its nature and purpose.

For images, specify an alt attribute:
<img src="catch.jpg" alt="John Smith catching the ball">

Please note that alt attributes should be relatively short. Where an image is used as a link, the alt should refer to the function of the link. Use the additional attribute londesc to provide a longer description. Where possible, rather than using an image to represent text, use text. It is also a good practice to name images logically; rather than image.jpg, name the file descriptively (e.g. umb_campus.jpg). Should you overlook an alt attribute, the file name will provide some clue as to the content.

For embedded media such as Flash presentations, provide a D-link or other hypertext link to a description.

When a non-text item is used inconsequentially, such as an icon, it is acceptable to set the alt attribute to a space:
<img src="icon.jpg" alt=" ">

However, you may want to consider why you are using an image if it is inconsequential. Even icons should have some meaning. Perhaps you have a mailbox icon in front of email addresses. In this case, you might consider an alt attribute of "mail icon."

Why is this important

At its heart, the Web is a text-based medium. While many browsers exist that allow for graphic, audio and multimedia features to be displayed via the Web, there are many browsers that do not display these non-text features. Examples of such browsers include those found on cell phones and PDA devices such as Palm Pilots.

In addition to the fact that not all browsers accept graphics and audio, there are many people who use the Web who cannot see or properly interpret images. Those who have no or low vision, rely on text alternatives for information and navigating a Web site.

Text also is a common denominator among many technologies that interact with the Web. For example, a search engine cannot read an image, but it can read an alt attribute. Using descriptive alts might also help your ranking on a search engine.