Patent attributes
Methods, apparatus and articles of manufacture (e.g., computer readable media) to detect watermark modifications are disclosed. Example apparatus disclosed herein include means for encoding a first watermark in a first media signal obtained from an output of a media device to obtain a second media signal encoded with the first watermark and a second watermark, the second watermark already encoded in the first media signal obtained from the output of the media device. Disclosed example apparatus also include means for decoding the first watermark and the second watermark from the second media signal to determine a first metric corresponding to the first watermark and a second metric corresponding to the second watermark. Disclosed example apparatus further include means for outputting, based on the first metric and the second metric, an indication of whether the second watermark has been modified.
