Since we installed iPhoto '09, our family has spent hours sitting around the computer, searching for photos of the kids, and teaching the computer what each of us looks like. We found a lot of old photos we had forgotten. We laugh at the mismatches. We try to understand the algorithms. This is one of the most entertaining programs that Apple has ever created.

Google's Picasa technology is far creepier. Instead of starting with a photo of someone you know and searching for all the similar matches, Google takes every photo that you've uploaded to Picasa, searches them all for faces, then "clusters"these faces into groups of, supposedly, the same people. You then go through each group and tell Google who a person is--including his or her full name, nickname, and e-mail address.

In fact, Google's clustering isn't all that great. It frequently puts different people in the same cluster, and it will make lots of different clusters for the same person. And unlike iPhoto, which could easily match photos of our 12-year-old daughter with her photos as a toddler, Google thought that the children were different people. But Google's user interface is pretty easy to employ, the matching task is strangely compelling, and before you know it, you'll have every one of your photos tagged with all the real names and e-mail addresses of each person that the photo features.

This real-name tagging is what makes Google's face recognition so creepy. Remember, all these photos aren't on your computer: they're on Google's server. And because e-mail addresses are unique, Google could use the tagged photos from all its Picasa users to create a global database matching photos to e-mail addresses. Doing so would not even violate Google's privacy policy, so long as Google only uses this information to make its service "better" and does not make the database generally available.

But what's really unsettling about Google's service is that it doesn't just stop at your friends. Before you know it, Google is asking you to identify all those other faces in your photographs--the people standing in the background, the faces in the crowds, even the faces on posters. This is certainly keeping with Google's corporate mission "to organize the world's information and make it universally accessible and useful." But is that what we really want from a photo-sharing website?

Our iPhoto experiences have been a delight: we've been excited and pleased to find so many pictures of our kids, family, and friends--and even ourselves. On the other hand, when we used the advanced tagging feature in Google's Picasa, we felt as though we were intelligence analysts working in the windowless lab of some totalitarian government.

We believe that consumer-driven face-recognition technology will fundamentally change public-policy debates about biometrics and mass video surveillance. After September 11, nobody really understood how this technology worked, what it got right, and what it got wrong. But before the end of this year, millions of Americans will have first-hand experience with some of the very best face-recognition systems ever deployed. Once the family-photo novelty wears off, we'll be watching to see if iPhoto and Picasa users ask their government to regulate this technology--or accelerate its deployment.