from six.moves import cStringIO as StringIO from PIL import Image def response(flow): if flow.response.headers.get("content-type", "").startswith("image"): try: s = StringIO(flow.response.content) img = Image.open(s).rotate(180) s2 = StringIO() img.save(s2, "png") flow.response.content = s2.getvalue() flow.response.headers["content-type"] = "image/png" except: # Unknown image types etc. pass