1) be sure to put in your environment file (inside your initializer)
config.gem "paperclip"
2) make sure your form_form has multipart set to true like this:
<% form_for @photo, :html => { :multipart => true } do |f| %>
3) if using passenger, you must put this in config/initializers/paperclip.rb:
if RAILS_ENV == "development"
Paperclip.options[:image_magick_path] = '/opt/local/bin/'
end
Paperclip.options[:image_magick_path] = '/opt/local/bin/'
end
(Make sure your imagemagick binaries are really in /opt/local/bin/. You can type /opt/local/bin/convert -v to check. I would recommend the MacPorts installation of ImageMagick and re-install if you are unsure.)