It sounds like the wrong identify
command (which is part of ImageMagick) is being called (or, perhaps, it isn't installed at all). Can you confirm the path to this command on your server using:
which identify
Once you've determined where this command is installed (e.g. /usr/local/bin
) then you can tell Paperclip about it by adding the following to your environment.rb (or production.rb etc) file:
Paperclip.options[:command_path] = '/usr/local/bin/'
(this is for Paperclip 2.2 and above. If you're using an earlier version you should use :image_magick_path
not :command_path
)