how to crop an image using rectangale overlay and touch on iphone

Question

Hey Everyone,

I am looking for a good tutorial or sample code, that would show how to crop an image taking from iphone camera

something in lines of

http://img192.imageshack.us/img192/8930/customcropbox.jpg

but you would control the corners with your fingers

any tip would be greatly appericated, as i am new to iphone dev.

Thanks, Amir