Patent ID: 8538069

Claim:
A method for recovering a spatial fingerprint from a sequence of digital video frames, the sequence including marked frames, each marked frame including marked groups, each marked group having markable positions, comprising: determining, for each frame, whether the frame is one of the marked frames by: computing, for each markable position in each marked group, a first diagonal DCT transform energy; computing, for each marked group, a total transform energy; computing, for each markable position in each marked group, a ratio of the first diagonal DCT transform energy to a residual, wherein the residual for the markable position is the total transform energy for the marked group to which the markable position belongs minus the first diagonal DCT transform energy for the markable position; computing, for each marked group, an accumulated total of the ratio by summing the ratio for each markable position in the marked group; computing, for each marked group, a quality ratio of a second maximum of the accumulated total of the ratio to a maximum of the accumulated total of the ratio; and identifying the frame as one of the marked frames when the quality ratio for each marked group in a first subgroup of the marked groups is less than a threshold value; determining whether the maximum of the accumulated total of the ratio is maintained for each marked group in the first subgroup of a number of successive marked frames; and recovering the spatial fingerprint from the number of successive marked frames.