As by today the first phTagr plugin is released: The DupFinder plugin finds media duplicates and merges the copies to one master media.
This plugin is very helpful if first lower quality media are uploaded to phTagr and the original data are uploaded on a later stage.
Example Scenario: Bob is traveling and want to upload his new vacation images as quick as possible. However, the Internet connection at the NetCafe is slow and upload of all original media is time consuming. Bob selects the best images and creates preview of it, which he uploads to phTagr. While Bob continue to travel his friends can tag the image and write comments.
When Bob arrives at home he uploads the original media and merges the tags and comments of the previews to the original.
See the wiki page of DupFinder for more details.