Further Description (16th February 2008)
(Another response to: Too much accessibility - the rise and fall of the LONGDESC.)
By “see the link” I meant “see” in the literal sense. A user who can view the image directly has no need for a link taking them to a description of what they just saw, afaict. A user who can’t see necessary details can zoom in with a screen magnifier or browser zoom.
Just as “[D]” links won’t fit a professional design, “Image Description” links won’t. longdesc neatly avoids this problem by letting the UA provide appropriate UI for it.
In text browsers, author styling is all but absent. These could create a “[D]” or “Image Description” link next to each image which uses longdesc.
Right-clicking an image and selecting Properties in Firefox provides various details in an Element Properties window. Including the value of longdesc, when present. This can be copied and pasted into the Address bar, making longdesc available without screen reader software in one browser already. Making this a hyperlink would be more convenient.
There is a longdesc extension which adds a View Image Longdesc item to the context menu. Any graphical UA could implement this in any operating system which supports context menus. Naming the item View Image Description might be more user-friendly.
A UA without convenient access to useful and standard HTML features can be updated by its vendor. A website which uses longdesc correctly and helpfully is already doing the right thing; it should not change.
Providing features via strange and unusual means makes supporting the web harder for UAs. CSS hacks and IE7 are a recent example. Using features correctly and then encouraging UAs catch up is a more robust strategy, imho.