Okay, so i\'ve got paperclip working, and I\'m trying to use the built in validator to make sure that the file uploaded
Obviously you solved this for yourself a long time ago, but for anyone who is looking for the answer, there is actually a way to do it within the provided validation.
Simple add your message like so:
validates_attachment :avatar,
:content_type => { :content_type => /image/, :message => "Avatar must be an image" },
:size => { :in => 0..2.megabytes, :message => "Avatar must be less than 2 megabytes in size" }