For all istructions refers to git://github.com/Squeegy/fleximage. I add a rails3_view.rb to manage template in rails3.

#rails3_view.rb

module ActionView

module TemplateHandlers
  class Rails3View < TemplateHandler
    include Compilable
    class TemplateDidNotReturnImage < RuntimeError #:nodoc:
    end

    def compile(template)
      "      @template_format = :flexi\n      controller.response.content_type ||= Mime::JPG    \n      result = \#{template.source}\n      requested_format = (params[:format] || :jpg).to_sym\n      begin\n        # Raise an error if object returned from template is not an image record\n        unless result.class.include?(Fleximage::Model::InstanceMethods)\n          raise TemplateDidNotReturnImage, \".flexi template was expected to return a model instance that acts_as_fleximage, but got an instance of instead.\"\n        end\n        # Figure out the proper format\n        raise 'Image must be requested with an image type format.  jpg, gif and png only are supported.' unless [:jpg, :gif, :png].include?(requested_format)\n        result.output_image(:format => requested_format)\n      rescue Exception => e\n        e\n      end\n      CODE\n    ensure\n      GC.start\n    end\n  end\nend\n"

end