Otherwise it fail with :

Traceback (most recent call last):
  File "/usr/local/lib/python2.6/dist-packages/tornado/stack_context.py", line 209, in _nested
    yield vars
  File "/usr/local/lib/python2.6/dist-packages/tornado/stack_context.py", line 180, in wrapped
    callback(*args, **kwargs)
  File "/usr/local/lib/python2.6/dist-packages/thumbor/loaders/http_loader.py", line 37, in return_contents
    callback(response.body)
  File "/usr/local/lib/python2.6/dist-packages/thumbor/handlers/__init__.py", line 226, in handle_loader_loaded
    callback(normalized, engine=engine)
  File "/usr/local/lib/python2.6/dist-packages/thumbor/handlers/__init__.py", line 116, in callback
    Transformer(self.context).transform(after_transform_cb)
  File "/usr/local/lib/python2.6/dist-packages/thumbor/transformer.py", line 87, in transform
    self.smart_detect()
  File "/usr/local/lib/python2.6/dist-packages/thumbor/transformer.py", line 141, in smart_detect
    detectors[0](self.context, index=0, detectors=detectors).detect(self.after_smart_detect)
  File "/usr/local/lib/python2.6/dist-packages/thumbor/detectors/face_detector/__init__.py", line 35, in detect
    self.next(callback)
  File "/usr/local/lib/python2.6/dist-packages/thumbor/detectors/__init__.py", line 27, in next
    next_detector = self.detectors[self.index + 1](self.context, self.index + 1, self.detectors)
TypeError: __init__() takes exactly 3 arguments (4 given)