Integration with Imagefield Extended module.

Any module may implement hook_insert_widgets() to specify which fields that widget provides. Insert will then pick up those fields with JavaScript and make them available as replacements in the insert-image.tpl.php file, which you can override in your theme. Take a look at imagefield_insert_widgets() in includes/imagefield.inc, which could be modified and placed into either a custom module or directly into imagefield_extended.module to make it so that Insert could utilize the fields provided by that module.