Security documents with hidden digital data

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CUT AND MASK PORTION OF SIGNAL OR IMAGE
BELIEVED TO BE SUSPECT
(ONLY IF ENTIRE SIGNAL OR IMAGE IS NOT SUSPECT)

X

PROCURE ORIGINAL DIGITAL SIGNAL OR
IMAGE AND CUT AND MASK TO ROUGHLY
THE SAME LOCATION OR SEQUENCE

X

VISUALLY RESCALE AND REGISTER THE CUT-OUT
SUSPECT SIGNAL TO THE CUT-OUT ORIGINAL SIGNAL

X

RUN THROUGH SEARCH PROGRAM WITH MEAN
SQUARED ERROR AS CRITERIA AND X OFFSET, Y OFFSET,
AND SCALE AS THE THREE VARIABLES

APPLY X OFFSET, Y OFFSET, AND SCALE TO CUT-OUT SUSPECT,
THEN RESAMPLE ONTO EXACT GRID AND CUT-OUT
OF ORIGINAL SIGNAL

X

RUN THROUGH SEARCH PROGRAM WITH MEAN
SQUARED ERROR AS CRITERIA AND DC OFFSET, GAIN, AND
GAMMA AS THE THREE VARIABLES; APPLY TO SUSPECT

X

SUBTRACT ORIGINAL FROM SUSPECT,
GIVING DIFFERENCE SIGNAL OR IMAGE

STEP THROUGH ALL N RANDOM INDEPENDENT SIGNALS, MASKED AS ORIGINAL AND CROSS-CORRELATED WITH DIFFERENCE SIGNAL IN IMMEDIATE NEIGHBORHOOD OF REGISTRATION POINTS

X

FIND 0 AND 1 LEVEL BY AVERAGING FIRST FOUR 0101 CODE VALUES

X

ASSIGN EITHER AO OR A 1 TO EACH CROSS-CORRELATION RESULT DEPENDING ON PROXIMITY TO THE AVERAGES OF PREVIOUS STEP

CHECK RESULT AGAINST SECURED IDENTIFICATION NUMBER

X

PROSECUTE IF IT MATCHES? OR AT LEAST SEND
A NASTY LETTER DEMANDING RECOMPENSE