An expansion to the United States Federal Bureau of Investigation's existing fingerprint database to include facial recognition has raised concerns among privacy advocates, due to its ability to contain images of innocents as well as criminals.
The FBI's next generation identification (NGI) biometric database contains over a hundred million individual records of people's fingerprints.
It being expanded to feature much more biometric information such as palm prints, voice signatures, iris scans and facial recognition, the agency said, in order to more quickly and accurately identify individuals.
Controversially, the NGI database will contain facial recognition data of millions of non-criminal citizens, documents obtained by the Electronic Frontier Foundation under the US Freedom of Information Act reveal.
Some 4.3 million images for non-criminal purposes will be in the database by next year as part of employers' background checks, which represents a threat to privacy, the EFF said.
The introduction of the NGI means the FBI would link its criminal and non-criminal databases for the first time.
Every record would have searches running against them, the EFF said, meaning non-criminal citizen's facial images could end up being searched as part of criminal investigations.
It said this raises the risk of innocent people being implicated as criminal suspects simply because their images are in the system.
The FBI is yet to identify what a further one million images in the "special population cognisant" and "new repositories" categories will be used for, according to the documents.
The recommended 0.75 megapixel resolution of the images addes to EFF's concerns, which it said is too low for accurate recognition.
Some 13.6 million images are already in the NGI, representing between seven and eight million people. Around half of US states are currently participating in the FBI's NGI program.