This is a highly configurable photo tagging plugin. It’s primely for tagging people on photos but it can also be used to create notes, but you will need to adapt the form part a little bit. The code is really clean and easy to understand, it follows the jquery plugin recommendations.
jTag is a free jQuery plugin that allows you to give a image tagging system on your site. You can add more information to your images and offer a more interactive experience to users.