This code worked for me
UIImage *backButtonImage = [UIImage imageNamed:@"back.png"];
UIButton *backButton = [UIButton buttonWithType:UIButtonTypeCustom];
[backButton addTarget:self action:@selector(backButtonPressed) forControlEvents:UIControlEventTouchUpInside];
[backButton setBackgroundImage:backButtonImage forState:UIControlStateNormal];
[backButton setFrame:CGRectMake(0, 0, 30, 30)];
UIBarButtonItem *backBarButton = [[UIBarButtonItem alloc] initWithCustomView:backButton];
[backBarButton setAction:@selector(backButtonPressed)];
self.navigationItem.leftBarButtonItem = backBarButton;
-(void)backButtonPressed{
[self.navigationController popViewControllerAnimated:YES];
}