photo tagging software

[Sam Fielder]

I am looking for a photo tagging program. similar to the google image 
labeler, but applicable to private photos. I have a shared photo archive 
  with several users updating and using the same archive, I would like 
to harness their abilities to tag the collection, but need some 
direction on what to use. The google solution seemed very elegant, where 
the users could compete to collaborate.

thanks

Sam