What user interface element would I use to take and crop a photo on the iPhone?

I'd like to be able to take a photo f开发者_如何学JAVArom the iPhone's camera, select a polygon within that photo, crop the photo to match, and then fit the resulting image to the screen.

What user interface element would you suggest for me to start doing this?

I'm a Java programmer and just getting started with the iPhone, so I'm not sure what to use.

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You should start by looking at sample code from Apple for UIImagePickerController to start getting the image. When you are comfortable with that you can start thinking about how to crop the image.