One day in 2005, a mother in Evanston, Ill., joined Flickr. Then she more or less forgot her account existed. Years later, their faces are in a database that's used to test and train some of the most sophisticated artificial intelligence systems in the world. The pictures of Chloe and Jasper Papa as kids are typically goofy fare: grinning with their parents; sticking their tongues out; costumed for Halloween. None of them could have foreseen that 14 years later, those images would reside in an unprecedentedly huge facial-recognition database called MegaFace.

One day in 2005, a mother in Evanston, Ill., joined Flickr. Then she more or less forgot her account existed. Years later, their faces are in a database that's used to test and train some of the most sophisticated artificial intelligence systems in the world. The pictures of Chloe and Jasper Papa as kids are typically goofy fare: grinning with their parents; sticking their tongues out; costumed for Halloween. None of them could have foreseen that 14 years later, those images would reside in an unprecedentedly huge facial-recognition database called MegaFace.