Prior to the release of the new SDK there has been some buzz about Apple finally providing access to live camera data:
I've been reading through Apple's documentation but have not found any reference to this. Now that the NDA has been lifted, does anyone know where this new functionality is documented?
Have a look at the the AV Foundation framework specially the AVCapture* classes.
This is thoroughly demonstrated in the WWDC 2010 session video 409: Using the Camera with AV Foundation. If you download the WWDC sample code, you'll find three or four sample applications that show how to use the various aspects of live camera capture and processing.
As Shaji points out, all of this is done through the AV Foundation framework using the new capture classes AVCaptureSession, AVCaptureInput, AVCaptureDevice, and AVCaptureOutput.