>> rackup

config.ru

# config.ru
require 'rack'
require 'gdk_pixbuf2'

class AvatarClone
  def call(env)
    request = Rack::Request.new(env)  
    case request.request_method
    when 'GET'
      begin
        filename = "./avatar/#{request.path.split('/')[1]}.jpg"
        return [200, 
                {'Content-type' => 'image/jpeg'},
                [Gdk::Pixbuf.new(filename).scale(80, 80).save_to_buffer("jpeg")]]
      rescue
        Rack::Response.new("Not Found", 404)
      end
    else
      Rack::Response.new("Bad Request", 400)
    end
  end
end

run AvatarClone.new