Setting a Custom Image for a Back Button on UINavigationBar

I am trying to set a custom image for the back button that automatically gets place onto a navigation bar when a new view is pushed onto the stack.

I have tried adding the following in the viewDidLoad of the parent viewController:

[[UIBarButtonItem appearance] setBackButtonBackgroundImage:[UIImage imageNamed:@"BackButton.png"] forState:UIControlStateNormal barMetrics:UIBarMetricsDefault];

I have also tried the following:

UIBarButtonItem *btn = [[UIBarButtonItem alloc] initWithImage:[UIImage imageNamed:@"BackButton.png"] style:UIBarButtonItemStyleBordered target:nil action:nil];
    self.navigationItem.backBarButtonItem = btn;

Using UIAppearance produces quite strange results:

try this code

UIButton *backBtn = [UIButton buttonWithType:UIButtonTypeCustom];  
UIImage *backBtnImage = [UIImage imageNamed:@"BackBtn.png"]  ;  
[backBtn setBackgroundImage:backBtnImage forState:UIControlStateNormal];  
[backBtn addTarget:self action:@selector(goback) forControlEvents:UIControlEventTouchUpInside];  
backBtn.frame = CGRectMake(0, 0, 54, 30);  
UIBarButtonItem *backButton = [[UIBarButtonItem alloc] initWithCustomView:backBtn] ;  
self.navigationItem.leftBarButtonItem = backButton;

then define goback method like this

- (void)goback
{
    [self.navigationController popViewControllerAnimated:YES];
}