The facial recognition app Clearview AI is not welcome in Canada and the company that developed it should delete Canadians’ faces from its database, the country’s privacy commissioner said on Wednesday.

“What Clearview does is mass surveillance, and it is illegal,” Commissioner Daniel Therrien said at a news conference. He forcefully denounced the company as putting all of society “continually in a police lineup.” Though the Canadian government does not have legal authority to enforce photo removal, the position — the strongest one an individual country has taken against the company — was clear: “This is completely unacceptable.”

Clearview scraped more than three billion photos from social media networks and other public websites in order to build a facial recognition app that is now used by over 2,400 U.S. law enforcement agencies, according to the company. When an officer runs a search, the app provides links to sites on the web where the person’s face has appeared. The scope of the company’s reach and law enforcement application was first reported by The New York Times in January 2020.

Mr. Therrien, along with three regional privacy commissioners in Canada, began an investigation into Clearview a year ago, after the article on the company was published. Privacy laws in Canada require getting people’s consent to use their personal data, giving the government grounds to pursue an inquiry. Authorities in Australia and the United Kingdom are jointly pursuing an inquiry of their own.

Dozens of law enforcement agencies and organizations across Canada used the app, according to the commissioners, including the national Royal Canadian Mounted Police. One Canadian law enforcement officer told The Times last year that it was “the biggest breakthrough in the last decade” for investigating child sexual abuse crimes. “Thousands of searches” were conducted, a report from the commissioners said, but only one agency was paying for the app, mainly because a number of groups used it through a free trial.

According to the commissioners’ report, Clearview said that it did not need consent from Canadians to use facial biometric information, because that information came from photos that were on the public internet. There is an exception in the privacy law for publicly available information. The commission disagreed.

“Information collected from public websites, such as social media or professional profiles, and then used for an unrelated purpose, does not fall under the ‘publicly available’ exception,” according to the report. The commissioners objected to the images being used in a way that the posters of the photos hadn’t intended and in a way that could “create the risk of significant harm to those individuals.”

Clearview AI said that it planned to challenge the determination in court. “Clearview AI only collects public information from the Internet which is explicitly permitted,” Doug Mitchell, a lawyer for Clearview AI, said in a statement. “Clearview AI is a search engine that collects public data just as much larger companies do, including Google, which is permitted to operate in Canada.”

The commissioners, who noted that they don’t have the power to fine companies or make orders, sent a “letter of intention” to Clearview AI telling it to cease offering its facial recognition services in Canada, cease the scraping of Canadians’ faces, and to delete images already collected.

That is a difficult order: It’s not possible to tell someone’s nationality or where they live from their face alone.

Hoan Ton-That, the chief executive of Clearview AI, said Wednesday that because of the inquiry, the company stopped operating in Canada last July, but had no plans to proactively delete Canadians from its database.

The company has previously taken pains to delete faces after running afoul of local privacy laws. Last year, Clearview was sued in Illinois for violating that state’s Biometric Information Privacy Act, which says that companies must get people’s consent before using images of their faces. Clearview tried to delete Illinois residents’ faces by, for example, looking at photo metadata and geographical information. It also allows state residents to request removal by uploading photos of themselves via an “opt-out form.”

Mr. Ton-That said Clearview allows Canadians to opt out of the database the same way.

Mr. Therrien was not satisfied with that solution. “You realize the irony of the remedy, requiring individuals to provide further personal information about themselves,” he said.

Mr. Ton-That said he was eager to fight the finding in court. “This is a simple issue of public information and who has access to it and why,” he said. “We don’t want a world where it’s just Google and a few other tech companies accessing public information.”