'Original' is the name of the image variation whose full path you need, other possible values are e.g. 'small', 'large' or whatever other aliases you have in your image.ini.
If you need other information about an image check the documentation for the content of an image attribute (which is an imagealiashandler for the respective image): http://ez.no/doc/ez_publish/technical_manual/3_8/reference/objects/ezimagealiashandler
