Allow Subscribers to Tag Photos

I am creating a reunion website that will contain the photographs of over 2,800 people. Each file has a number associated with it, but I need the help of the site participants to identify the individuals portrayed. I have broken the pictures into albums or galleries but cannot figure out how to allow the participants to enter the name of the individual portrayed. The pictures are stored in my media library as well as on google+ and photobucket. Is there a plugin to do this? I am a novice wordpress user so the solution can’t be too complicated.