Fifteen years ago, 100,000 football fans streamed into the Raymond James Stadium in Tampa for Super Bowl XXXV. They would witness the wild card Ravens handily defeat the Giants, take in a halftime show that featured N'Sync and Aerosmith, and have their faces digitally scanned, analyzed, and cross-referenced with a database of wanted and suspected criminals. They, uh, didn't know about that last part until after the fact.

A few days after the game, thanks to the news media and the American Civil Liberties Union, word got out that the Super Bowl had been a testing grounds for new facial recognition software that mapped and cataloged the facial features of everyone in attendance. The ACLU, and many members of the public, were disturbed.

"Facial recognition was a very new, untested technology and it was still kind of science-fictiony," said Jay Stanley, a senior policy analyst at the ACLU. Stanley wasn't yet at the ACLU at the time, but he subsequently penned a report on law enforcement's use of facial recognition technology.

Keep in mind this is early 2001, in a pre-9/11, pre-Snowden America. The idea of having your biometric data collected was as far-fetched as the idea that you might be being spied on.

"There was a great deal of concern, a 'Big Brother is watching,' kind of thing," said Jane Castor, a former Chief of the Tampa Police Department. Castor was a sergeant in 2001, and remembers the public response though she was not directly involved in the facial recognition program.

"There was a great deal of concern, a 'Big Brother is watching,' kind of thing."

Castor told me when it came to the Super Bowl, the decision to use facial recognition software wouldn't have been up to the local police—for a huge, national event like that, security is passed off to the federal level—but they would have been involved.

After the game, police said the technology had helped identify 19 individuals in the crowd who had outstanding warrants, but the public remained skeptical. Still, just a few months later, Tampa was offered a free one-year trial of the face recognition software. The city opted to give it a try, setting up face-scanners in the downtown entertainment district called Ybor City.

"The technology was just expanding so rapidly and we wondered: is there a benefit or is there not? So we tested it out," Castor said. "It's like the body worn cameras today. There are a lot of potential positive aspects but there's so much we don't know yet until those are tested in the community."

The idea was that the software might be able to catch wanted criminals, or alert police if known offenders, like sexual assault convicts, were hanging out in the area. But it wasn't advanced enough to be able to identify and make these kinds of warnings, Castor said, adding she couldn't remember a single case when the software was useful.

It's one thing if someone is standing perfectly still, looking at a camera. Trying to capture and analyze faces moving on a busy, crowded street is a completely different challenge, and one that the software was evidently not up to. The collected images are also useless without a database with which to compare them, and there was debate at the time over an appropriate database, Castor said: the local prison system? The DMV? The FBI's most wanted? After a year or so, the program was ultimately scrapped, both in Ybor City and by the Super Bowl, which opted for old fashioned human surveillance going forward.

Still, the software continued to be developed and refined, and just last year we saw glimmers of its reemergence in law enforcement: US customs is experimenting with facial recognition software at an airport in DC. But in an age when being spied on is almost an expectation, and people happily scan their thumbprints for Apple or have their identity programmed into Facebook, will facial recognition creep back into use without much of a fight this time?

Maybe not.

Stanley pointed out that while Facebook may have powerful facial recognition technology, using Facebook is opt-in (and it's pretty obvious your face is being documented, all you need to do is tag a photo). Surreptitiously being scanned when you're walking down the street is another issue entirely, Stanley said.