code: def _find_only_image_column(sframe):
      
      from turicreate import Image
      return _find_only_column_of_type(sframe, target_type=Image,
                                       type_name='image', col_name='feature')
docs: Finds the only column in `sframe` with a type of turicreate.Image. 
      If there are zero or more than one image columns, an exception will 
      be raised.