16. The non-transitory computer readable storage medium of claim 15 , wherein the content descriptors comprise at least: a large scale subset of the content descriptors characterizing larger scale features of the content piece; and a small scale subset of the content descriptors characterizing smaller scale features of the content piece.
16. The non-transitory computer readable storage medium of claim 15 , wherein the content descriptors comprise at least: a large scale subset of the content descriptors characterizing larger scale features of the content piece; and a small scale subset of the content descriptors characterizing smaller scale features of the content piece. 18. The non-transitory computer readable storage medium of claim 16 , wherein the content descriptors at each respective scale are contained in the large scale subset of the content descriptors.