Efficient decoding of watermarking schemes in the presence of false alarms

We treat the problem of recovering the correct message if extra bits (false alarms) are added to the body of the message at random locations. This situation is common for some watermarking systems with selective embedding which is typical when the human visual (or audio) system is incorporated to enhance the quality of the watermarking system. We propose an efficient decoding scheme for convolutional codes using some modifications of the Viterbi algorithm. Extra states are added to represent the possible false alarms and a new expansion algorithm of the modified trellis diagram is proposed. The simulation results show the high efficiency of our algorithm in detecting random false alarms with high rates.