I use the following code to customize the back button on the navigation bar throughout my application:
UIImage *backButton = [[UIImage imageNamed:@\"backButt
[[UIBarButtonItem appearanceWhenContainedIn:[UIImagePickerController class], nil] setBackButtonBackgroundImage:[UIImage imageNamed:@"blank-button"] forState:UIControlStateNormal barMetrics:UIBarMetricsDefault];
this is the correct way