Thanh Trung, a resident of the northern province of Vinh Phuc, lost his wallet with important documents including his ID card and his driver's license on January 1. He planned to redo all the paperwork needed to get new documents.

On January 3, he received a Facebook notification about tag suggestions from a stranger's post.

"A woman who lives dozens of kilometers away found my wallet and shared a lost and found post on Facebook. The facial recognition option picked up my face from the photo of my driver's license and sent me a notice," he said.

The face recognition setting, made available in 2017, notifies account holders if their photos are used by someone else by comparing and analyzing images to help users know if they appear in other posts.

Trung said he had turned on this feature and posted his photos on Facebook occasionally, so the system recognized his face.

The feature was previously called "tag suggestion" but later changed to "face recognition" after it received public backlash on privacy concerns. Users have the option to disable this service.