I was checking out the CIDetector API in iOS5, specifically using it with an AVCaptureSession to detect faces in video.  I’d never played with the AV Foundation framework before, but it was pretty straight forward to hook up the front camera on the phone as an AVCaptureDevice and get the frames through an AVCaptureVideoDataOutput.

However I ran into issues when trying to get CIDetector to find faces in the CIImage from the video.  Eventually I came across the Apple SquareCam sample which contained the solution!

Because it might help someone else Googling and it took me forever to find. I could no longer login to my account after a few system crashes due to bad RAM during the login process.

If you are suffering from a so-called “login loop” in Mac OS X 10.7 Lion - ie. you login to your account and then suddenly you’re back at the login prompt again - your LaunchServices cache might be corrupt.