Heroku: Running imagemagick with paperclip
Do you have the RMagick gem included in your app on Heroku? It's necessary for interfacing between your Ruby code and ImageMagick.
ImageMagick is part of the Heroku platform by default, but you have to specify that you need the RMagick gem for your app. I'm guessing you have this installed locally so it works there, but it's missing from your Gemfile or gems manifest (depending on Heroku stack version).
Try to remove the Paperclip.options[:command_path] = "/path/to/" when deploying to heroku.
This solved the issue for me.