# File lib/ec2/ec2.rb, line 330
    def modify_image_attribute(image_id, attribute, operation_type = nil, vars = {})
      params = {'ImageId'   => image_id,
                'Attribute' => attribute}
      params['OperationType'] = operation_type if operation_type
      params.update(hash_params('UserId', vars[:user_id].to_a)) if vars[:user_id]
      params.update(hash_params('UserGroup', vars[:user_group].to_a)) if vars[:user_group]
      params.update(hash_params('ProductCode', vars[:product_code])) if vars[:product_code]
      link = generate_request("ModifyImageAttribute", params)
      request_info(link, RightBoolResponseParser.new(:logger => @logger))
    rescue Exception
      on_exception
    end