This script in conjunction with jQuery allows just that… Very simple and fairly unobtrusive.

If you wanted to add captions to all images (from their longdesc, title or alt attributes) within <div class=”content”/> you could do:

$('div.content').addCaptions();

Which produces something like this:

jQuery Add Captions - Screenshot (Like this!)

No styling is carried out by the script itself, so you’ll have to add in some extra classes, but in the zip file should be everything you need to get started (including jQuery 1.3.2 minified).

Download

Edit: Added to the work blog too.

Update: I have updated the script, see this post.