@implementation UINavigationBar (UINavigationBarCustomDraw)

- (void) drawRect:(CGRect)rect {
     
     [self setTintColor:[UIColor colorWithRed:0.5f
                                    green: 0.5f
                                    blue:0 
                                    alpha:1]];
     
     if ([self.topItem.title length] > 0 && ![self.topItem.title isEqualToString:@"Back to ..."]) {
          [[UIImage imageNamed:@"Header_1px.png"] drawInRect:rect];
          
          CGRect frame = CGRectMake(0, 0, 320, 44);
          UILabel *label = [[[UILabel alloc] initWithFrame:frame] autorelease];
          [label setBackgroundColor:[UIColor clearColor]];
          label.font = [UIFont boldSystemFontOfSize: 20.0];
          label.shadowColor = [UIColor colorWithWhite:0.0 alpha:1];
          label.textAlignment = UITextAlignmentCenter;
          label.textColor = [UIColor whiteColor];
          label.text = self.topItem.title;
          self.topItem.titleView = label;
          
     } else {
               [[UIImage imageNamed:"Header.png"] drawInRect:rect];
               self.topItem.titleView = [[[UIView alloc] init] autorelease];
     }
}

@end

source: http://www.developers-life.com/custom-uinavigationbar-with-image-and-back-button.html