修改UIImagePickerController的navigationBar的Title、Item和背景图

在UIImagePickerControllerDelegate方法中编写：

- (void)navigationController:(UINavigationController *)navigationController didShowViewController:(UIViewController *)viewController animated:(BOOL)animated {
    UINavigationBar *navigationBar = navigationController.navigationBar;
    [navigationBar setBackgroundImage:[UIImage imageNamed:@"background.png"] forBarMetrics:UIBarMetricsDefault];
    navigationBar.tintColor = [UIColor whiteColor];
    [[UINavigationBar appearance] setTitleTextAttributes:@{NSForegroundColorAttributeName:[UIColor whiteColor]}];
}