code: def _ProcessImage(self, tag, wall_time, step, image):
      
      event = ImageEvent(wall_time=wall_time,
                         step=step,
                         encoded_image_string=image.encoded_image_string,
                         width=image.width,
                         height=image.height)
      self.images.AddItem(tag, event)
docs: Processes an image by adding it to accumulated state.