If you want to make a rails application that deals with pictures then paperclip may be the plugin of your choice. You can install paperclip via github
rails plugin install git://github.com/thoughtbot/paperclip
After installation I tried to generate the picture handling to my rails application by running:
rails generate paperclip Modellname picturemodell
Rails threw an error no such file to load — cocaine
Simply install the cocaine gem gem install cocaine
Run bundle install
Be a happy camper!