It seems in iOS 6, a drop shadow is automatically added to the navigation bar even when you set a custom background image. I\'m pretty sure this wasn\'t the case with iOS 5
I came across this SO question when trying to get nav bars to look the same between iOS6 and iOS7.
The answer I found worked was simply to use:
NSMutableDictionary *titleBarAttributes = [NSMutableDictionary dictionaryWithDictionary: [[UINavigationBar appearance] titleTextAttributes]];
[titleBarAttributes setValue:[NSNumber numberWithInt:0] forKey:UITextAttributeTextShadowOffset];
[[UINavigationBar appearance] setTitleTextAttributes:titleBarAttributes];
ie: set the shadow offset to zero.