A method and apparatus for adding watermark data to an input signal is provided. For this method watermark data is embedded into the input signal by modulating elements of the input signal to predefined relationships in reference to other elements of the input signal. By using referential relationships and by using patterned sequences, one or more bits of data can robustly be embedded. Further, a method and apparatus for recovering data embedded by the method and apparatus of the present invention, are also provided. To recover the embedded data, differences between elements of the input signal to reference elements of the signal are calculated and checked against predefined relationships. Predefined relationships thus found are used to recover pieces of the embedded information.