At least half of American adults are pictured in a facial recognition network used by law enforcement, according to a report published Tuesday by Georgetown University’s Center on Privacy and Technology, which recommends prompt adoption of privacy protections.

The report says a minimum of 117 million adults have been entered into such a network because they are licensed to drive in one of 26 states that allow police to search driver's license photos for face matches. And it’s possible many more people are affected.

Four additional states were not counted toward the total, with the center unable to verify reports in the Washington Post and Cincinnati Enquirer that Indiana, Massachusetts, Mississippi and South Dakota allow police to scan driver's license photos.

Though many unknowns remain, the report uses about 100 responses to public record requests to build a more complete picture of the emerging technology's use.

In addition to distinct state systems, the FBI has a large facial recognition network of more than 400 million photos belonging to an unknown number of people featured in mugshots or striking a non-criminal pose for civil purposes.

The Government Accountability Office's May report on the FBI's facial recognition unit said the unit had access to driver’s license photos of 16 states. The new report says FBI agents in Florida – not one of the 16 – additionally have direct access to the Pinellas County Sheriff’s Office facial recognition system of Florida drivers license photos.

Sixteen states allow the FBI's facial recognition unit access to state driver's license photos, according to a May report from the Government Accountability Office. A new report says FBI field agents in Florida also can search a database of the state's driver licenses for matches. GAO

The Pinellas system is used for 8,000 monthly searches without audits, a requirement of any criminal suspicion, a publicly released use policy or disclosure to the local public defender's office, says Clare Garvie, a fellow at the center and a report co-author.

The Georgetown report relays that state and local agencies have various policies, with many having no known safeguards for First or Fourth Amendment rights. The center crafted a scorecard hosted on the website perpetuallineup.org to track varying policies.

Alvaro Bedoya, executive director of the Georgetown center and another co-author of the report, said during a Tuesday conference call with reporters that "this is not business as usual – law enforcement has never created a national biometric database that is populated primarily by law-abiding people."

Of particular concern, Bedoya said, is that real-time facial recognition technology appears to be increasingly sought after by police, with agencies in Chicago, Dallas and West Virginia buying or announcing an intention to buy the technology.

“We have to ask ourselves, does that look like America: A world where everyone’s face is scanned as they walk on a sidewalk, a world where police can secretly identify people attending a protest just by taking a photo of them? We don’t think it does,” Bedoya said.

A majority of information within reach of the FBI's facial recognition network, which includes the FBI's primary database and those of other federal and state agencies, comes from non-criminal sources. Georgetown University’s Center on Privacy and Technology

The report says facial recognition technology appears to be less accurate with young black Americans, citing a 2012 study co-authored by the FBI. Though that may seem a boon for privacy-conscious African-Americans, who are disproportionately likely to engage with law enforcement, a technology expert on the conference call said this could result in many innocent members of the demographic being targeted.

Jonathan Frankle, a report co-author and doctoral candidate at the Massachusetts Institute of Technology, said the technology generally works either by identifying potential matches that exceed a similarity threshold or by matching top results without a threshold.

“You would think there’s a nice privacy benefit if African-Americans are rejected from the system,” Frankle said, “but we can’t say anything about who’s getting pushed up a list. … It could end up having innocent people move up the list.”

The FBI co-authored study cited in the report found that three facial recognition algorithms tested for accuracy were 5 to 10 percent less reliable on black versus white Americans.

Garvie said the researchers were aware of four algorithms sold by companies to law enforcement agencies, with other firms having a foot in the market developing interfaces.

The report recommends efforts to better understand the accuracy of the technology and a prohibition on searches of driver’s license photos without clear legislative approval.

Neema Singh Guliani, a legislative counsel at the American Civil Liberties Union, said the use of facial recognition technology could chill the exercise of First Amendment rights, adding on the conference call that authorities should stop using the technology until safeguards are in place.

“We don’t expect the police can identify us when we are walking into a mosque, when we’re attending an AA meeting, when we’re seeking help at a domestic violence shelter,” Guliani said. “And the ability of police to do this without appropriate safeguards raises a number of civil liberties concerns.”