Image has a LONGDESC attribute that is not valid for one of the following reasons:

• It points to a non-existing local file or web resource
• It points to a non-HTML resource

Make sure the link specified by the LONGDESC attribute is working.

Since not many browsers at the moment support the LONGDESC attribute, you may also want to place a so-called D-link near the image. A D-link is a normal textual link with label "D" pointing to an HTML page providing a full image description. Example:

    <IMG src="chart.gif" alt="chart of beverages distribution"
    longdesc="chart.html"><A href="chart.html">D</A>

Placing a rich textual description such as a caption close to the image is another viable solution. In such a case, you will not need the LONGDESC attribute or the D-link.

The ALT attribute cannot be used to provide a full-length description of the content of an image. Think of a diagram, a histogram, a chart, or a product picture in an online catalogue. To describe its content, you need more flexibility.

The LONGDESC attribute can be used to provide a long description of the associated image. By including the attribute LONGDESC="any_HTML_file" in your IMG tag, you can link the image to the HTML file containing a formatted description of the image. The long description (unlike the ALT attribute) can contain HTML code, with links to other resources, formatting instructions, and more.

However, since not many browsers at the moment support the LONGDESC attribute, you may also want to place a so-called D-link near the image. A D-link is a normal textual link with a label "D" pointing to an HTML page providing a full image description. Example:

    <IMG src="chart.gif" alt="chart of beverages distribution"
    longdesc="chart.html"><A href="chart.html">D</A>

Placing a rich textual description such as a caption close to the image is another viable solution. In such a case, you will not need the LONGDESC attribute or the D-link.

Adding a good alternative description to images is very important today because many users can't take advantage of graphics. They include users of cellular phones, PDAs, and browsers installed in cars.