Hi CHI...
Here's a summary of the replies to my recent question about the use of alt
tags. Thank you so much! This was very helpful. :)
- Alt tags should always be used, whether or not image captions are also
included. They provide useful information to people that turn images off in
their browsers. Search engines check them and can improve site findability.
Screen readers for the disabled read them. Without the alt text, screen
readers just read linked graphics as "Link." (For more information about
designing for accessibility, see the W3C guidelines at
http://www.w3.org/wai/.)
- Alt tags should always be descriptive. For example, on a Web page with
numerous photos of different company logos, the alt tags should say
something useful, like "Mercedes-Benz," not "Logo."
- You can't depend on alt tags always appearing, therefore, alt tags should
not be used to replace image captions where they are needed. According to
more than one listserv respondent and based on a test on Chris H's Mac, alt
tag pop-up boxes do not work on Macs. You will, however, see the alt tags
on Macs if you turn the images off, and search engines and screen readers
can still read them.
- Alt tag pop-ups should not interfere with the user's ability to see other
critical information on the page. (See the left nav bar at
http://www.att.com for an example of alt tags getting in the way of the
readability adjacent text.)
- Alt tags can mitigate the poor usability of long downloads times. Users
will see alt tags before the images download and can click on alt tag links
without having to wait. (See http://www.monster.com for an example of
this.)
- Alt tags should be turned 'off' if it is determined that they are not
wanted (which should only be in very exceptional situations). Turning alt
tags off is done by inserting a 'blank' or alt tag, as in ALT=" ". Users
with disabilities who 'view' pages with screen readers will be very
thankful, since for them this means a silent alt tag. Such readers go
through all text in a page and read it to the user. If the reader comes
across an IMG tag, it will look for the ALT tag and read that description.
If it does not come across an ALT tag, it will read the name of the image,
which can become pretty aggravating to listen to with auto-generated image
names for sliced graphics like 'img__screen_r1_c1', 'img__screen_r1_c2',
'img__screen_r1_c3' etc.
*************************************
Jodi Bollaert
Usability Architect
Compuware Digital Development Center
http://www.compuware.com
1(800)292-7432, ext. 55520
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