alt attribute is intended to be a
short alternative for the image, and shouldn’t be used for
lengthy descriptions of the image. The attribute that’s used to provide a
pointer to further information is
Unfortunately, it’s so poorly supported that it’s almost unusable (see
below for more information).
longdesc attribute refers to a text file
<img src="giant-prawn.jpg" alt="The Giant Prawn at Ballina" longdesc="prawn.txt"/>
This attribute takes as its value the URL for a file that contains the extra descriptive text, most likely a simple .txt file.
longdesc attribute has almost no practical use,
even with today’s good, standards-aware browsers. Despite the best
intentions, no browser on the support charts makes it clear to the user
when extra information is available for the image in the form of a
descriptive text file, and this level of indifference toward the attribute
is likely to continue. Even the technology that would benefit the most
from the presence of this attribute—assistive technology such as screen
readers—is oblivious to the presence of a
Only Firefox appears to demonstrate even a basic level of awareness of the
attribute: if you right-click on the image and choose
file location is visible next to the Description
title, as shown in Figure 1.
longdescshows in Firefox’s contextual menu as the Description
A much safer option is to avoid this attribute altogether, and simply to create a link that anyone can access or see, perhaps linking from picture caption text.