A free facial recognition tool that allows people to find photos of themselves or others from the Internet has sparked criticism from privacy activists.
PimEyes describes itself as a privacy tool to help prevent misuse of images.
But Big Brother Watch said it could "allow state surveillance, commercial monitoring and even stalking on an unimaginable scale."
It comes when Amazon decides to stop using facial recognition for a year.
The Polish PimEyes website was created in 2017 as a hobby project and marketed last year. It currently has 6,000 registered users.
Attention was drawn to an article published in Medium.
The website allows people to upload any image for free and will find matching images from all over the web, drawing on publicly accessible sites like Tumblr, outlets and blogs.
Silkie Carlo, director of Big Brother Watch, told the BBC: "Seeing this powerful surveillance technology marketed for individuals is chilling. It is ripe for stalking and puts women and children at unprecedented risk."
In response, PimEyes said: "Our privacy policy prevents people from using our tool for this case. Any tool could be used the wrong way."
He told the BBC that he categorically did not use images downloaded from social media, despite the fact that the BBC found images of his reporters that had been uploaded to Facebook and Twitter.
"If you found faces that were published only on Facebook, it means someone else posted it somewhere else. We only explore websites that agree on their crawl rules," he said in an email.
The use of social media images has put the facial recognition company ClearviewAI in difficulty. He has accumulated more than three billion photos from Facebook, Twitter and YouTube, used by the FBI, the Department for Internal Security and 600 other law enforcement agencies around the world to identify suspects.
All three social networks have asked to stop doing it.
PimEyes offers a premium service that allows people to post up to 25 pictures of different people and receive alerts whenever new photos are uploaded online. It currently has 350 active users of this service.
He told the BBC that the website's premise was to help people "fight for their online privacy," including finding fake profiles, leaked images and using unauthorized photos.
He acknowledged that it worked with the police force, fueling Paliscope, a software tool used by law enforcement agencies.
But he removed a reference on his website about police dark web search.
According to the PimEye website, images uploaded to the site "are never saved or indexed". Instead he says he uses a one-sided fingerprint - the main features - which is encrypted and temporarily saved on his servers.
Amazon ban
Facial recognition technology became increasingly controversial when multiple police forces around the world adopted the tools.
Numerous studies question the accuracy of the technology, suggesting that it works particularly badly when identifying black people.
In the wake of protests over the killing of George Floyd and for police reform requests, IBM and Amazon have both blocked the use of facial recognition technology.
In Amazon's case, the police use of its Rekognition software has been suspended for a year to allow the U.S. government to decide how it wants the technology to be used in the future.
