Apple is to scan all photos and videos on iPhones as they are uploaded to the cloud in a bid to find child sexual abuse images and videos.
Technology will look for images it believes match child sexual abuse which will then be flagged to human operators - who can then contact law enforcement.
But there are fears about privacy as people's pictures and videos are monitored - and fears the technology could be expanded to monitor things such as political activity.
Apple says the latest versions of its iPhone and iPad operating systems, released later this year, will include the new scanning technology.
The system compares images and videos to an existing database provided by child protection agencies, to look for similarities.
Apple says the technology will find edited and similar images as well as identical matches.
A spokesman said: "Before an image is stored in iCloud Photos, an on-device matching process is performed for that image against the known CSAM hashes.
Apple says the technology has an "extremely high level of accuracy and ensures less than a one in one trillion chance per year of incorrectly flagging a given account".
Apple says that it will manually review each report to confirm there is a match. It can then take steps to disable a user's account and report to law enforcement.
Matthew Green, a security researcher at Johns Hopkins University, said: "Regardless of what Apple's long-term plans are, they've sent a very clear signal. In their (very influential) opinion, it is safe to build systems that scan users' phones for prohibited content."
For more stories from where you live, visit InYourArea.
