현재화면 캡쳐하기

//img에 현재 화면이 캡쳐 된다.

UIImage *img;

UIGraphicsBeginImageContext(self.view.frame.size);

GContextRef context = UIGraphicsGetCurrentContext();

[self.view.layer renderInContext:context];

img = UIGraphicsGetImageFromCurrentImageContext();

UIGraphicsEndImageContext();