a visor with (very, very) bright IR LEDs over your face could hide you from camera sensors; i've seen something like this used to defeat license plate scanners, and i know that LEDs have greatly improved power efficiency in the last decade, but i don't have any experience in this kind of thing. maybe someone can pick up this idea and run with it if it's feasible.

this wouldn't defeat something like gait detection though: http://www.geradts.com/html/Documents/gait.htm

I am sure the camera would detect a person with an unreadable face and alert the cops or something

This is an interesting link: http://gajitz.com/about-face-defeat-face-recognition-softwar...

Purportedly there are non-obvious sunglasses/frames that attempt to make it more difficult for such scanners to operate. The success rate of these devices ranges from "not at all" to "seems to work".

Decentralized observation, citizens watching citizens, citizens watching the powers that be- and if necessary decentralized anti-terrorism surveilance. That is acceptable.

Depending on the details of how the system is used and the availability of political remedies (or lack thereof), I think direct action would be justified.

A particulate filter mask, maybe combined with a cheap plastic sunshade visor?

Be a female muslim who chooses to wear a burka.