Apple unveiled plans to scan US iPhones for images of child abuse, drawing applause from child protection groups but raising concern among some security researchers that the system could be misused by governments looking to surveil their citizens. Apple said its messaging app will use on-device machine learning to warn about sensitive content without making private communications readable by the company. The tool Apple calls “neuralMatch” will detect known images of child sexual abuse without decrypting people’s messages. If it finds a match, the image will be reviewed by a human who can notify law enforcement if necessary. But researchers...