Information signals such as grayscale images or audio signals are
represented as a sequence of PCM signal samples. To embed auxiliary data
in the least significant bits of the signal, the samples are slightly
distorted. There is a so-termed "rate-distortion function" (20) which
gives the largest embedding rate R given a certain distortion level D. It
appears that the efficiency of prior art embedding schemes such as LSB
replacement (21,22) can be improved. The invention discloses such
embedding schemes (23,24). According to the invention, the signal is
divided into groups of L (L>1) signal samples (x). For each group of
signal samples, a vector of least significant portions (x mod n) of the
signal samples is created. For n=2, the vector comprises the least
significant bit of each signal sample. The syndrome of said vector (as
defined in the field of error detection and correction) represents the
embedded data. Only one (or a few, in any case less than L) signal
sample(s) of a group needs to be modified so as to achieve that the
vector assumes a desired syndrome value.