In a scene in the 2002 movie “Minority Report,” set in 2054, Tom Cruise’s character walks through a subway station lined with camera lenses and talking digital billboards. “John Anderton!” one of them calls out to him. “You could use a Guinness right about now.”

Such a setup will be technologically feasible much sooner than 2054. Already, digital billboards and signs scan faces to gather demographic information for marketing purposes. A wide array of companies, from Adidas to Whole Foods, has rolled out systems that predict gender and age and then deliver targeted ads. Intel says its AIM (Audience Impression Metrics) suite of software, which powers the Adidas and Whole Foods systems, can predict gender with 94 percent accuracy and age range with 90 percent accuracy.

Facebook, whose users upload around 200 million photos every day, boasts perhaps the widest reach of facial recognition software, which, unlike facial detection software, matches images to identities and tends to store data, therefore presenting clearer privacy concerns. The social network uses the technology to recognize faces in photos and suggest who should be tagged in them.

As databases, algorithms and camera lenses improve, facial recognition accuracy is growing. In facial recognition tests performed in controlled settings by the National Institute of Standards and Technology, false-negative rates fell from 79 percent in 1993 to .003 percent in 2010, halving every two years...