Patent ID: 7336841

Claim:
A method comprising: receiving a video stream comprising a plurality of image frames, each image frame comprising a matrix of pixels; selecting a subset of the image frames; for each image frame in the subset determining a sub-fingerprint for the image frame, wherein determining the sub-fingerprint for the image frame includes: computing a discrete cosine transformation (DCT) block for a pixel block surrounding a pixel, said DCT block having coefficients, computing an estimation of a variance of the coefficients, setting a variance value in a variance matrix with the estimation of the variance, wherein the value is set at a position in the variance matrix corresponding to the pixel position in the image frame matrix, determining a minimum variance value in a signature window of the variance matrix enclosing the pixel position, and setting a first predetermined value representing the minimum variance in a constellation matrix at a position corresponding to the minimum variance value and setting all other positions in the signature window to a different predetermined value; and assembling the sub-fingerprints into a fingerprint for the video stream.