5. The method of claim 4 wherein said signature and said parametized signals each comprise a plurality of digital words, each digital word of said signature and said parametized signals being derived by comparing the average luminances of selected areas of a frame of said segment to the average luminance of at least one reference area, each of said selected areas providing a bit of said digital word.
8. The method of claim 5 wherein said at least one reference area is, for each of said selected areas, a different preselected area of said frame.