Some iPhone 4 users have seemingly uncovered a "creepy" glitch in the handset's FaceTime video-calling function.

The glitch has come to light after several users reported erratic behaviour by their handset when using the FaceTime function on the Apple Discussion Forums.

9to5Mac reports that random images - some not even photographs stored in the iPhone's camera roll but seemingly taken surreptitiously - show up on screen to some users of FaceTime.

"My boyfriend and I have both recently experienced this problem several times - when one of us is calling the other via FaceTime, an old picture freezes on our screen, while the person receiving the call only sees a black screen. It's kind of creepy, because it brought up photos of both of us at work, where I have used FaceTime a few times but he never has," the thread's originator said.

"It's not terribly inconvenient, but it's definitely unsettling, where is seems that even if we haven't taken a picture or used FaceTime, the camera is keeping images," she continued.

Another user reported the problem to Apple, who told him to restore his iPhone and set it up as a new device. "The problem didn't go away after that, so they actually had me return it to an Apple store and swap it out for a new one. This also didn't help," he wrote.

If the reports are correct, then a number of unsettling privacy issues raise their head, as 9to5Mac points out. Given that the images that appear can't be found on the handset it is difficult to know why it was taken, whether it has been sent elsewhere, or if it could be the work of a rogue app.