iOS - How to customize the crop rect in UIImagePickerController with allowsEditing on?
You have to implement a custom cropping GUI to get anything other than the default, as stated in the Camera Programming Topics for iOS:
"When using built-in editing controls, the image picker controller enforces certain options. For still images, the picker enforces a square cropping as well as a maximum pixel dimension. For movies, the picker enforces a maximum movie length and resolution. If you want to let the user edit full-size media, or specify custom cropping, you must provide your own editing UI."