Nielsen and Watermarks

Engadget reports on a new technology for more accurately measuring local viewing activity via set-top boxes and watermarks.  More information and press release at the link.  Particularly interesting to me was the concept of a watermark.   An invisible, but detectable code embedded into an image that can be interpreted by a sensor.  We examined the concept for on consumer package and pallet scanning.  Not sure if this is relevant to the Nielsen example, but does a watermark implicitly give your permission to be scanned?

Also interesting is that this effort " ... will lay the groundwork to collect ratings for online, tablets and other platforms ... "