I'm trying to use ruby-exiv2, the ruby bindings to the Exiv2 image 
metadata library. The docs are really sparse, though. In fact, this is it:

Basic usage:

   > gem install RubyInline
         > gem install ruby-exiv2
         > irb -r rubygems

         require 'exiv2'
         @img = Exiv2::Image.new("a.jpg")
         puts @img["Exif.Photo.PixelXDimension"]
         @img["Exif.Photo.PixelXDimension"] = 2048
         @img.save

Version 1.3 introduces dynamic accessors:

     require 'exiv2'
     @img = Exiv2::Image.new("a.jpg")
     puts @img.Exif.Photo.PixelXDimension
         @img.Exif.Photo.PixelXDimension = 2048
         @img.save


There's a list of tags in the exiv2 website (DateTimeOriginal, etc). But 
I'd really like to be able to make the 'img' object (to use the above 
example) give me a list of keys (or key-like tags) so I know what's 
available (especially since not all images will have the same tags--for 
example, some will and some won't have gps coordinates embedded).

Does anyone have any experience with ruby-exiv2? I couldn't find a mailing 
list for it...

Paul