用 tornado 写过一个
流程大概就是取参数去读本地图片, 再缩放尺寸吐出去

import os
import magic
import StringIO
from PIL import Image
from PIL.ExifTags import TAGS
import tornado.web

class img(tornado.web.RequestHandler, tornado.web.StaticFileHandler):
  def get_mime(self, path):
    mime = magic.Magic(mime=True)
    return mime.from_file(path)

  def send_img(self, ret, mime_type):
    self.set_header("Content-Type", mime_type)
    self.set_header('Content-Length', len(ret))
    self.finish(ret)

  def resize(self, path, size):
    mime_type = self.get_mime(path)
    if not mime_type or not os.path.exists(path) or not os.path.isfile(path):
      raise tornado.web.HTTPError(404)
    img = Image.open(path)
    _size = tuple([int(s) for s in size.split('x')])
    img.thumbnail(_size, Image.ANTIALIAS)
    buffer = StringIO.StringIO()
    img.save(buffer, mime_type[6:])
    ret = buffer.getvalue()
    self.send_img(ret, mime_type)

  def get(self, path, includ_body=True):
    path = self.parse_url_path(path)
    abspath = os.path.abspath(os.path.join(self.root, path))
    size = self.get_argument('s', None)
    if size:
      self.resize(abspath, size)
    else:
      tornado.web.StaticFileHandler.get(self, path, includ_body)

用IOstring和make_response生成图片响应，搜一下有一篇flask生成验证码的博客文章，你可以参考下