Gait analysis (how a person moves around) is definitely also used these days, so the masks may make it a tad more difficult, but certainly not impossible.

You know how you can tell that a person walking in the distance is your friend, even though you can't see their face at that distance? Yeah, so can algorithms.

There’s also gait analysis, so unless the rioters can disguise how they walk, it will be difficult to hide.