@classmethod
def from_image(klass, img):
    """ Class method to create new instance of own class from `img`

        Parameters
        ----------
        img : ``spatialimage`` instance
           In fact, an object with the API of ``FileBasedImage``.

        Returns
        -------
        cimg : ``spatialimage`` instance
           Image, of our own class
        """
    raise NotImplementedError()
