-So a script that will automatically parse post images and make them pop-ups.
-If an image is already contained within a link then the plugin would skip that image.
-Written for compatibility with current Wordpress version and future compatibility in general (as far as can be reasonably done).
In case it helps:
There is a plug-in called Simple Popup Images ( http://granades.com/simple-popup-images/ ) - however this relies on a post author manually clicking on a quicklinks button to insert the popup code.
There is a pop-up plugin for user biography which does seem to automatically parse content and insert a popup. ( http://www.dagondesign.com/articles/user-bio-popup-plugin-for-wordpress/ )