Patent ID: 7085395

Claim:
An apparatus for detecting and recovering data embedded in information material, the data having been embedded in the material using a transform domain representation of at least one of said data and said information material by arranging for the data to modulate a predetermined data sequence to form modulated data and combining said modulated data with said material, the apparatus comprising: a transform processor operable to transform the material into a transform domain representation of said information material, and a correlation processor operable to correlate transform domain data symbols bearing said modulated data from said transform domain representation with a reproduced version of said predetermined data sequence to form a correlation output signal and to recover said embedded data from said correlation output signal, wherein said correlation processor is operable to perform said correlation of transform domain data symbols with data symbols of the predetermined data sequence, for a plurality of start positions in said transform domain, said start positions representing at least one relative possible shift of said transform domain data, and if said shift of said transform data represents a loss or corruption of transform domain data symbols, omitting corresponding symbols from said predetermined data sequence in said correlation, said lost or corrupted transform domain data symbols and said corresponding symbols of said predetermined data sequence not being included in calculating the correlation output signal.