Convert the given image into a dict convertible to tf example.

def encode_example(self, image_or_path_or_fobj):
    """Convert the given image into a dict convertible to tf example."""
    if isinstance(image_or_path_or_fobj, np.ndarray):
      encoded_image = self._encode_image(image_or_path_or_fobj)
    elif isinstance(image_or_path_or_fobj, six.string_types):
      with tf.io.gfile.GFile(image_or_path_or_fobj, 'rb') as image_f:
        encoded_image = image_f.read()
    else:
      encoded_image = image_or_path_or_fobj.read()
    return encoded_image