可以通过获取AVCaptureConnection，然后调用setVideoOrientation:方法解决图像90°问题。

比如：显示AVCaptureVideoPreviewLayer

[[_videoPreviewLayer
 connection] 
setVideoOrientation:AVCaptureVideoOrientationLandscapeRight];

拍照，输出用AVCaptureStillImageOutput时，

outputPic
 = [[AVCaptureStillImageOutput alloc]init];
AVCaptureConnection
 * videoConnection = [outputPic connectionWithMediaType:AVMediaTypeVideo];
[videoConnection
setVideoOrientation:AVCaptureVideoOrientationLandscapeRight];

摄像，输出用AVCaptureMovieFileOutput时，

outputMovie
 = [[AVCaptureMovieFileOutput alloc] init]; 
AVCaptureConnection
 * videoConnection = [outputMovie connectionWithMediaType:AVMediaTypeVideo];

[videoConnection
setVideoOrientation:AVCaptureVideoOrientationLandscapeRight];