Mappa is an image mapping component for Joomla. With Mappa, you can upload any custom photo to your website and then add clickable locations to the image that display overlayed panels with detailed information.
In other words, if you upload a picture of your face, you can tag your eyes, ears, nose, and mouth. When the user clicks on your eyes, ears, nose, or mouth, a little popup will display your custom HTML.
Check it out here: http://dioscouri.com/joomla-extensions/mappa/download where you can also download it for the price of a tweet on Twitter or a post on Facebook.