US Patent 10102602 Detecting watermark modifications

Methods, apparatus, systems and articles of manufacture (e.g., physical storage media) to detect media watermark modifications are disclosed. Example watermark modification detection methods disclosed herein include encoding a second watermark in a media signal including a first watermark. Disclosed example methods also include detecting the first watermark and the second watermark in the media signal. Disclosed example methods further include, in response to detecting the first watermark and the second watermark, comparing a first strength metric determined for the first watermark and a second strength metric determined for the second watermark to determine whether the first watermark was modified prior to being encoded in the media signal.