How to show camera view in iOS4 SDK (without video/image capturing feature)

I would like to show camera view in iOS4 SDK, here are my requirements:

1. no need video/image capturing feature
2. need to overlay UIImage / UIImageView above the camera view
3. use as low memory as possible

I have seen several methods:

1. using AVCaptureSession
2. using UIImagePicke开发者_高级运维rController

Which is better? I tried UIImagePickerController methods, but it prompts memory warnings.