The W3C Accessibility Guidelines identify providing text equivalents for non-text elements in a web page as a top priority for making web pages accessible to all users.
The ALT attribute allows you to do this for images (within the <IMG> tag) and other non-text elements. As well as helping with accessibility, this also helps to make your site more search engine friendly since search engine spiders cannot otherwise glean any information from images.
One thing I tend to do is to write ALT text in a similar way for similar images – for all logos the ALT text begins with “Logo:”, for all photos the ALT text begins with “Photo:” and so on.
You can also add the LONGDESC attribute to provide more detail about a non-text element. The W3C states that the LONGDESC attribute can be used with the <IMG> and <FRAME> tags. (The LONGDESC attribute provides a link to a page providing further information – I’m not sure how well this is supported by different browsers). The ALT attribute can still be included to provide a title for the image.
Check out Free DIY SEO for more information on making pages search engine friendly.
