Fancybox is a tool for displaying images, html content and multi-media in a Mac-style “lightbox” that floats overtop of web page. It was built using the jQuery library.
This plugin inserts the necessary elements required to run Fancybox on your blog. It also groups images within posts using rel attributes. (Based on the code found on this forum thread)
To disable Fancybox per post: Add a custom field called ‘nofancybox’ and set it’s value to ‘true’. Instructions on how to add custom fields to posts can be found at this codex article.