code: def read_ring_images_index():
      
      meta = read_cumulative_iss_index()
      ringfilter = meta.TARGET_DESC.str.contains("ring", case=False)
      return meta[ringfilter]
docs: Filter cumulative index for ring images.
  
      This is done by matching the column TARGET_DESC to contain the string 'ring'
  
      Returns
      -------
      pandas.DataFrame
          data table containing only meta-data for ring images