Since your tracker is oriented towards web development, you might want to take a look at my work here, a Firefox addon for taking screen captures of a web page, marking it up with arrows, highlights, and then posting them to the the bug tracker.

This is the addon, http://ifdefined.com/BugTracker.NET.xpi

And it works with BugTracker.NET http://ifdefined.com/bugtrackernet.html

It was the first time I played with the firefox addon technology. I wouldn't recommend my technical approach, injecting a div into the page. If I were inspired to redo it, I would do something more XUL-ish. But I do think that making it fast and easy to capture/annotate/post screenshots is key to making it something people want to use.