[z2600]

But, aren't ecommerce sites collecting this information and more from your browsing? I don't think it's possible to say one is much better than the other, just that we expect tracking online, not in the real world.

[parhurs]

There is the point that in the "real world", social norms haven't yet adapted to the requirements of privacy (although you could also view it as societal norms allowing too much tracking). For example, if I wanted to use a mask to conceal my face from trackers, I would be ostracized. There are analogues in the virtual world of course, but it's usually harder in the physical world.

[beachbum8029]

This also works http://www.instructables.com/id/The-Invisible-Face-Mask-/

[BoorishBears]

They're even more accurate than facial recognition at building a profile of what demographic you fit in