But it's not just that Picasa has a better face-detection interface—it also has a better detection engine, meaning that it finds more matching faces than iPhoto, and it does so with unbelievable accuracy. A few weeks ago, in a comment on a column I wrote about Google's self-driving car, a reader named "nerdnam" sang the praises of Picasa's face detection. "I put about 90 years of family photos through it and it could match faces through infancy, childhood, middle age, and old age," the commenter wrote. "It wasn't defeated by costumes, wigs, going bald, or even Halloween makeup. It didn't match every single face, but of the ones it did, I think there was only [one] mistake."
How does Picasa perform so well? Lisa Conquergood, a product manager for Google Photos, says the program's face-detection analysis is similar to the technology behind Google Image search. To identify faces, Picasa measures key distances between prominent facial features, essentially reducing your mug to a number. To find matches, Picasa simply looks for other photos with similar numbers. Conquergood says that engineers are constantly testing the system to identify weak spots in its matching algorithm. Recently, they noticed that Picasa wasn't doing a great job identifying children's faces. The team expanded its pool of test photos to include a lot more pictures of young people, and Picasa's latest version is now a lot better at spotting kids.
Not just kids—babies! Nearly six weeks ago, my wife and I had our first child, and since then we've snapped hundreds and hundreds of the cutest baby pictures the world has ever seen. These photos show that our baby has changed remarkably over the span of his short life—he's gained half of his birth weight, his eyes have widened, his nose has grown, he's picked up a double chin, and he's gotten his first haircut. What's more, the shots reveal an astonishingly wide variety of facial expressions—my baby curls and purses his lips, scrunches his eyes, and strains and tenses his whole body, turning his forehead beet red. (Babies, I've learned, are born with lots of different facial expressions to express discomfort, but exactly zero to register pleasure or even mere contentment; happiness, it turns out, is something you've got to learn.) But even with all these challenges, Picasa is undaunted. However much my son's face changes as he grows, and whatever strange things he does with his eyes, nose, and mouth, Picasa always picks him out.
I will note one pet peeve with Picasa: It lacks Facebook integration. While iPhoto easily lets you upload pictures to the social network (which is by far the world's largest photo-sharing site), you need to download a plug-in to do so from Picasa. But that's a quibble. Looking at Picasa's stream of close-ups of my baby's face has become a good way for me to while away half a weekend—and if you give it a try, the same will happen to you, too.