B. Mann Consulting

The Gush developers have created something very similar to Flickr's notes capability:

We've released a web utility called FotoBuzz which allows you to annotate JPEGs using Flash on the client side and PHP/Python on the server-side. It's dirt easy to integrate into existing webpages. After including some CSS and JavaScript in the HTML head, all you have to do is add a single attribute to the image tag and it will do the rest for you.
Going Nowhere: FotoBuzz viewlet

Of course I have to think about putting this into Drupal somehow. Along with integrating Flickr directly (Jonas -- get off your ass and release that code!), this should do nicely.