Privacy concerns have been raised over the development of a facial recognition database by the FBI which could contain as many as 52 million images by 2015.
The Electronic Frontier Foundation (EFF) has said that it is concerned that images of innocent people will be stored alongside pictures of criminals.
The database is part of the FBI's biometric "Next Generation Identification" (NGI) programme, aimed at being implemented over the next few years.
As well as faces, the programme is being expanded to storing captured fingerprints, iris scans and palm prints. Although currently the fingerprints of criminals and innocent people are kept separately, photos (which the FBI will ask people to submit with their prints in the future) will be stored together.
"This means that even if you have never been arrested for a crime, if your employer requires you to submit a photo as part of your background check, your face image could be searched - and you could be implicated as a criminal suspect, just by virtue of having that image in the non-criminal file," said the EFF, according to the BBC.
The NGI programme already has 16 million images stored, and, warns the EFF, has the capability to grow that amount to 52 million.
Read more: The year the NSA hacked the world
The protest group has also highlighted research that showed the risk of falsely identifying someone as a criminal increases as a database holding sensitive information grows.
"This means that many people will be presented as suspects for crimes they didn't commit. This is not how our system of justice was designed and should not be a system that Americans tacitly consent to move towards," the EFF added.