Thursday 11 July 2002

Accessibility tip 18: Provide text equivalents for images

“The most important day of the series,” writes Mark Pilgrim and yes, it’s the crucial alt text:

Every single image on every single page of your site should have a text equivalent, so-called “alt text”, specified in the alt attribute of the <img> tag.

Not much to do here. I modified the alt text for the XML icon, as Mark suggested and changed the alt text for the ideograph in my banner from “Kokoro kanji” to “Site logo: xīn, the Chinese character for heart.” The latter change produced a brief moment of excitement—that perhaps only Professor Salo will appreciate—since it prompted me to find the correct “i with a macron” character (ī) for xīn. The Evolt Simple Character Entity Chart doesn’t have macron characters but they’re available at the Māori Spellchecker site. (I wonder now whether I’m being too smart by half. Do only Windows 2000 & XP and Mac OS X understand Unicode? It’s difficult to tell: on a Windows 98 machine it looks fine whereas on my old PowerPC running System 8.6 the macron appears after the “i” instead of above it.)

After my difficulty in manipulating list margins, I thought it prudent to do some addtional reading. I found the most useful of Mark’s references to be that provided by WebAIM (it includes recordings of the screen reader IBM Home Page Reader 3.0 reading the images). About alt text they say:

The general rule for the content of an alt attribute is that the alt attribute should provide a brief description of the function of the image. It is important to note here that that alt attribute should describe the function of the image which is not necessarily the same as a description of the appearance of the image…

Alternative text for images should be as succinct as possible. A good rule of thumb is to keep the alt attribute less then 15 words long. The reason for this is that users accessing the content with a screen reader or refreshable brailler will get the alt tag whether they want it or not. So if you add a very long description of the an image that the user has no interest in, they will still be forced to listen to the entire alt tag before proceeding on. If you need a longer description of the image, you should use the “longdesc” attribute or a “D” link to provide the content.

Mark might be referring to the longdesc attribute when he says: “We’ll discuss complex images on Friday.”

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Comments

You're way ahead of me. ;-)

Posted by Mark Pilgrim on 11 July 2002 (Comment Permalink)

It does not surprise me that Mac OS 8.x is unhappy about Unicode. Mr. Jobs was a mite late climbing on that particular bandwagon.

Posted by Dorothea Salo on 11 July 2002 (Comment Permalink)

[spam removed]

Posted by DAS on 27 April 2003 (Comment Permalink)

This discussion is now closed. My thanks to everyone who contributed.

© Copyright 2007 Jonathon Delacour