A system enables encoding of a removable mark into digital data, and
decoding of the mark from the digital data. The system comprises an
encoder and a decoder. The encoder includes a target area locator for
locating in digital data a predetermined pattern of values that represents
a flat area, and a marker for modifying values in the flat area to encode
a mark into the flat area. The decoder attempts to extract the mark from
the digital data. The decoder includes a mark area locator for locating a
predetermined pattern of values in digital data, and an unmarker coupled
to the mark area locator for examining the values to determine the state
of each value and extract an embedded mark from the predetermined pattern
of values.
