Kashmir Hill and Aaron Krolik:

The pictures of Chloe and Jasper Papa as kids are typically goofy fare: grinning with their parents; sticking their tongues out; costumed for Halloween. Their mother, Dominique Allman Papa, uploaded them to Flickr after joining the photo-sharing site in 2005.

None of them could have foreseen that 14 years later, those images would reside in an unprecedentedly huge facial-recognition database called MegaFace. Containing the likenesses of nearly 700,000 individuals, it has been downloaded by dozens of companies to train a new generation of face-identification algorithms, used to track protesters, surveil terrorists, spot problem gamblers and spy on the public at large. The average age of the people in the database, its creators have said, is 16.

“It’s gross and uncomfortable,” said Mx. Papa, who is now 19 and attending college in Oregon. “I wish they would have asked me first if I wanted to be part of it. I think artificial intelligence is cool and I want it to be smarter, but generally you ask people to participate in research. I learned that in high school biology.”