Using the tag for images

When you use the WordPress image uploader to include an image in your
post or page, a Description text box appears, in which you can enter a
description of the image. (We cover using the WordPress image uploader
in detail in Book IV, Chapter 3.) This text automatically becomes what’s
referred to as the <ALT> tag.

The <ALT> tag’s real purpose is to provide a description of the image for

people who, for some reason or another, can’t actually see the image. In a
text-based browser that doesn’t display images, for example, visitors see the
description, or <ALT> text, telling them what image would be there if they
could see it. Also, the tag helps people who have impaired vision and rely on
screen-reading technology because the screen reader reads the <ALT> text
from the image. You can read more about Web site accessibility for people
with disabilities at http://www.w3.org/WAI/intro/people-use-web.
php.
An extra benefit of <ALT> tags is that search engines gather data from them
to further classify the content of your site. The following code inserts an
image, with the <ALT> tag of the code in bold to demonstrate what we’re
talking about:

<img src=”http://yourdomain.com/image.jpg” alt=”This is an ALT tag within an
image” />

Search engines harvest those <ALT> tags as keywords. The WordPress
image uploader gives you an easy way to include those <ALT> tags without
having to worry about inserting them into the image code yourself. Just fill
out the Description text box before you upload and add the image to your
post. Book IV, Chapter 3 covers in-depth information on adding images to
your site content, including how to add descriptive text for the ALT tag and
keywords.