Playing around with Aperture 3, Apple’s advanced photo management software, I applied the faces feature to an album of photos taken at various zoos. Faces scans photos and identifies what it thinks are human faces. You can then identify the various faces to create collections for individuals among your photos. It’s fun, if imperfect.
The only “face” the application found among the zoo photos was this one, a tiger at the Denver Zoo. Gotta admit, an impressive face. The picture was taken in May 2004.