Fingerprinting Computers By Making Them Draw Images
Here’s a new way to identify individual computers over the Internet. The page instructs the browser to draw an image. Because each computer draws the image slightly differently, this can be used to uniquely identify each computer. This is a big deal, because there’s no way to block this right now.
EDITED TO ADD (7/22): This technique was first described in 2012. And it seems that NoScript blocks this. Privacy Badger probably blocks it, too.
EDITED TO ADD (7/23): EFF has a good post on who is using this tracking system — the White House is — and how to defend against it.
And a good story on BoingBoing.