UIImage *image = [self.faceDetectionView snapshot];
    if (image) {
        ALAuthorizationStatus authStatus = [ALAssetsLibrary authorizationStatus];
        if (authStatus == ALAuthorizationStatusRestricted || authStatus == ALAuthorizationStatusDenied){
            //无权限
            return;
        }
        [[[ALAssetsLibrary alloc] init] writeImageToSavedPhotosAlbum:image.CGImage metadata:nil completionBlock:^(NSURL *assetURL, NSError *error) {
            if (!error) {
                NSLog(@"Image saved succeed");
            }
        }];
    }