Swizzled UIImage imageNamed for iPhone 5

UIImage+Retina4.h

//
//  UIImage+Retina4.h
//  StunOMatic
//
//  Created by Benjamin Stahlhood on 9/12/12.
//  Copyright (c) 2012 DS Media Labs. All rights reserved.
//

#import <UIKit/UIKit.h>

@interface UIImage (Retina4)

@end

UIImage+Retina4.m

//
//  UIImage+Retina4.m
//  StunOMatic
//
//  Created by Benjamin Stahlhood on 9/12/12.
//  Copyright (c) 2012 DS Media Labs. All rights reserved.
//

#import "UIImage+Retina4.h"
#import <objc/objc-runtime.h>

static Method origImageNamedMethod = nil;

@implementation UIImage (Retina4)

+ (void)initialize {
    origImageNamedMethod = class_getClassMethod(self, @selector(imageNamed:));
    method_exchangeImplementations(origImageNamedMethod,
                                   class_getClassMethod(self, @selector(retina4ImageNamed:)));
}
                                                   
+ (UIImage *)retina4ImageNamed:(NSString *)imageName {
    NSLog(@"Loading image named => %@", imageName);
    NSMutableString *imageNameMutable = [imageName mutableCopy];
    NSRange retinaAtSymbol = [imageName rangeOfString:@"@"];
    if (retinaAtSymbol.location != NSNotFound) {
        [imageNameMutable insertString:@"-568h" atIndex:retinaAtSymbol.location];
    } else {
        CGFloat screenHeight = [UIScreen mainScreen].bounds.size.height;
        if ([UIScreen mainScreen].scale == 2.f && screenHeight == 568.0f) {
            NSRange dot = [imageName rangeOfString:@"."];
            if (dot.location != NSNotFound) {
                [imageNameMutable insertString:@"-568h@2x" atIndex:dot.location];
            } else {
                [imageNameMutable appendString:@"-568h@2x"];
            }
        }
    }
    NSString *imagePath = [[NSBundle mainBundle] pathForResource:imageNameMutable ofType:@"png"];
    if (imagePath) {
        return [UIImage retina4ImageNamed:imageNameMutable];
    } else {
        return [UIImage retina4ImageNamed:imageName];
    }
    return nil;
}

@end

UIImageRetina4.h

//
//  UIImage+Retina4.h
//  StunOMatic
//
//  Created by Benjamin Stahlhood on 9/12/12.
//  Copyright (c) 2012 DS Media Labs. All rights reserved.
//

#import <UIKit/UIKit.h>

@interface UIImage (Retina4)

@end

UIImageRetina4.m

//
//  UIImage+Retina4.m
//  StunOMatic
//
//  Created by Benjamin Stahlhood on 9/12/12.
//  Copyright (c) 2012 DS Media Labs. All rights reserved.
//

#import "UIImage+Retina4.h"
#import <objc/runtime.h>
#import <objc/message.h>

static Method origImageNamedMethod = nil;

@implementation UIImage (Retina4)

+ (void)initialize {
    origImageNamedMethod = class_getClassMethod(self, @selector(imageNamed:));
    method_exchangeImplementations(origImageNamedMethod,
                                   class_getClassMethod(self, @selector(retina4ImageNamed:)));
}
                                                   
+ (UIImage *)retina4ImageNamed:(NSString *)imageName {
    NSLog(@"Loading image named => %@", imageName);
    NSMutableString *imageNameMutable = [imageName mutableCopy];
    NSRange retinaAtSymbol = [imageName rangeOfString:@"@"];
    if (retinaAtSymbol.location != NSNotFound) {
        [imageNameMutable insertString:@"-568h" atIndex:retinaAtSymbol.location];
    } else {
        CGFloat screenHeight = [UIScreen mainScreen].bounds.size.height;
        if ([UIScreen mainScreen].scale == 2.f && screenHeight == 568.0f) {
            NSRange dot = [imageName rangeOfString:@"."];
            if (dot.location != NSNotFound) {
                [imageNameMutable insertString:@"-568h@2x" atIndex:dot.location];
            } else {
                [imageNameMutable appendString:@"-568h@2x"];
            }
        }
    }
    NSString *imagePath = [[NSBundle mainBundle] pathForResource:imageNameMutable ofType:@"png"];
    if (imagePath) {
        return [UIImage retina4ImageNamed:imageNameMutable];
    } else {
        return [UIImage retina4ImageNamed:imageName];
    }
    return nil;
}

@end

This needs an update for new iphones

Here you go with an updated version working for iPhone 6 and 6Plus !
https://gist.github.com/kevindelord/fe2e691d06ab745fbb00