Problems with alt-text:

why alt-text is not the simple solution for screen reader access that it is assumed to be: look at these problematic examples (with autoload images off):

Using the Height and Width attributes

When the following example is viewed with Netscape on a Macintosh, the image icons overlap the text anchors of other images making the text anchors and the alt-text unreadable. The height and width are set to 14.

When this page is viewed with Netscape on a Windows machine, the rightmost icons and text may be scrolled to the right of the current window. Once this happens a screen reader user may not know that this has happened. Even if they are aware that there is more information to display, it can be difficult for the user to access this information.

(View the orginal page this comes from)

In order to see at least one character of alt-text (in this example an asterisk) the width needs to be at least equal to 40. The height needs to be at least equal to 30 so that graphics on different lines do not overlap each others attached text anchors.