def __str__(self):
        return self._str(self.globals,self.locals)
helper function: given an image, return the json to pass back to the
dataset/ETHPy150Open ipython/ipython-py3k/IPython/external/Itpl/_Itpl.py/ItplNS.__str__--crossover with--dataset/ETHPy150Open torchbox/wagtail/wagtail/wagtailimages/views/chooser.py/get_image_json