You don't necessarily need to identify one amongst 1.3 billion. (requiring 30 bits of information out of the gait!) The context is a crowd of about 100 (10 - 1

You don't necessarily need to identify one amongst 1.3 billion. (requiring 30 bits of information out of the gait!) The context is a crowd of about 100 (10 - 1000), in which you are tracking a few percent, and you need to keep "eyes" on an individual, discriminating amongst a few others that have crossed is path. That said, I'd agree that it looks difficult to help distinguish individuals in a trained team.