Custom UITabBar background image not working in iOS 5 and later

iOS5 offers the UIAppearance Proxy.

Also, it's best practice to switch your code based on the capability (in this case it's respondsToSelector) instead of iOS version - that's a fragile assumption (who's to say it doesn't change in the future).

You can set it for just that instance or globally for all tab bars:

// not supported on iOS4    
UITabBar *tabBar = [tabController tabBar];
if ([tabBar respondsToSelector:@selector(setBackgroundImage:)])
{
    // set it just for this instance
    [tabBar setBackgroundImage:[UIImage imageNamed:@"tabbar_brn.jpg"]];

    // set for all
    // [[UITabBar appearance] setBackgroundImage: ...
}
else
{
    // ios 4 code here
}

//---- For providing background image to tabbar

UITabBar *tabBar = [tabBarController tabBar];
if ([tabBar respondsToSelector:@selector(setBackgroundImage:)])
{
    // ios 5 code here
    [tabBar setBackgroundImage:[UIImage imageNamed:@"PB_MD_footer_navBg_v2.png"]];

}
else
{
    // ios 4 code here

    CGRect frame = CGRectMake(0, 0, 480, 49);
    UIView *tabbg_view = [[UIView alloc] initWithFrame:frame];
    UIImage *tabbag_image = [UIImage imageNamed:@"PB_MD_footer_navBg_v2.png"];
    UIColor *tabbg_color = [[UIColor alloc] initWithPatternImage:tabbag_image];
    tabbg_view.backgroundColor = tabbg_color;
    [tabBar insertSubview:tabbg_view atIndex:0];

}

After reviewing various articles, I found the answer for anyone that's having the same problem:

UIImageView *imageView = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"tabBG.png"]];

if ([[[UIDevice currentDevice] systemVersion] floatValue] > 4.9) {
    //iOS 5
    [self.tabBarController.tabBar insertSubview:imageView atIndex:1];
}
else {
    //iOS 4.whatever and below
    [self.tabBarController.tabBar insertSubview:imageView atIndex:0];
}

[imageView release];

Works like a charm! Enjoy.