In image upload meta box is it possible to add the option to select images that are already in the media library?
Currently, you can do that only with thickbox_image field.
Gonna try to do this with the new media uploader found in WordPress 3.5. Found a tutorial here that may help: http://mikejolley.com/2012/12/using-the-new-wordpress-3-5-media-uploader-in-plugins/
image-advanced added, which now has this functionality thanks to the new image uploader in WP 3.5