(supplemental to Andrew Johnson's response)
The linked Apple.com post includes 3 or 4 different solutions, most of which only "half" work. I think the most elegant/effective of them is this one:
@implementation UINavigationBar (CustomImage)
- (void)drawRect:(CGRect)rect {
UIImage *image = [UIImage imageNamed: @"NavigationBar.png"];
[image drawInRect:CGRectMake(0, 0, self.frame.size.width, self.frame.size.height)];
}
@end
HOWEVER ... it's not good-practice ObjC to od that as a category (should be an override), and it has some problems of its own.
So, a more general and powerful solution is here:
http://samsoff.es/posts/customize-uikit-with-method-swizzling