1. A method for embedding a structured watermark into data, defined by a plurality of samples, wherein the data has a format for a frequency domain representation of the data comprising an ordered set of a plurality of frequency domain values, the method comprising: defining an ordered set of variations to be applied to the frequency domain values, wherein each variation has a value defined by the structured watermark; defining an irregular mapping from positions in the ordered set of variations to positions in the ordered set of frequency domain values; and modifying each frequency domain value by the variation mapped by the irregular mapping to the position of the frequency domain value in the ordered set of frequency domain values.