Check out this guy's blog. He is working on a thesis to research counter technology to privacy invasions... some of his other posts show suggestions for face makeup to defeat facial recognition systems.
As you may know from previous posts, I am somewhat interested in such things, seeing as how many of these technologies can be abused by governments to make life hard for legitimate protesters.
So further to his ideas for reducing "true positives", I'd like to suggest a camoflage pattern for urban clothing that consists of lots of "false positive" facial elements designed to slow a facial recognition algorithm down and ensure that people are incorrectly tracked in locations they have never visited. Here is a hastily-bodged version of what I'm on about (imagine a crowd of people wearing T-shirts with this pattern):
Combined with other stuff like this InfraRed hat, I think we could have a cool kit to take back some privacy.