Friday Sync-Up: Collecting "Faceprints"

Every Friday, I present a topic or question for our merry band of thinkers, leaders, and pirates to discuss in an open thread. Here is this week’s conversation starter:

Advancing facial recognition technologies are helping to stop criminals like child abusers and violent extremists. But they are also increasingly collecting “faceprints” in public spaces and being used for marketing and other commercial applications.

Question: What is a reasonable expectation of privacy when it comes to facial recognition deployment in public spaces? And what, if any, constraints should be put on this technology?