code: def remove_thumbnail(self, thumbnail):
          
          if thumbnail in self._thumbnails:
              index = self._thumbnails.index(thumbnail)
              self._thumbnails.remove(thumbnail)
          self.layout().removeWidget(thumbnail)
          thumbnail.deleteLater()
          thumbnail.sig_canvas_clicked.disconnect()
          thumbnail.sig_remove_figure.disconnect()
          thumbnail.sig_save_figure.disconnect()
  
          # Select a new thumbnail if any :
          if thumbnail == self.current_thumbnail:
              if len(self._thumbnails) > 0:
                  self.set_current_index(min(index, len(self._thumbnails)-1))
              else:
                  self.current_thumbnail = None
                  self.figure_viewer.figcanvas.clear_canvas()
docs: Remove thumbnail.