LONDON: British and Australian privacy watchdogs said on Friday they had launched a joint probe into a US software startup able to match images of unknown faces to photos scraped from social media sites.

The UK's Information Commissioner's Office (ICO) said it had opened the investigation, alongside the Office of the Australian Information Commissioner (OAIC), into "the personal information handling practices" of Clearview AI.

The California-based firm has built a stockpile of more than three billion photos which it says it has already signed up to share with hundreds of law enforcement agencies worldwide.

"(We) have opened a joint investigation into the personal information handling practices of Clearview AI Inc., focusing on the company's use of 'scraped' data and biometrics of individuals," ICO said in a statement.

"The investigation highlights the importance of enforcement cooperation in protecting the personal information of Australian and UK citizens in a globalised data environment." The move follows the opening of a similar probe by Canada's privacy watchdog earlier this year.