11. The method defined in claim 8 , further comprising assigning placeholder data to those regions for which said extracting is not carried out.
8. The method defined in claim 7 , wherein the particular video frame in the query video stream is divided into a plurality of regions and wherein said extracting at least one feature for each of a plurality of regions of the particular video frame in the query video stream is carried out for less than all of the regions of the particular video frame in the query video stream.