“While we had no way to test their claims, the developers of Blink! say that the app has no false positives.”

Here’s something to try. Record some video of yourself on a laptop (not the computer you have Blink! on).

Then start the video playing and set it in front of the web cam. Will Blink! figure out that this isn’t really you? You may need to run the video in mirror image to give the right view to the webcam (or maybe not – my brain is a bit fuzzy on that).