Using IOSurface to take screenshot in iOS7 in game

I'm trying to take screenshots from background using IOSurface, here's my code

IOMobileFramebufferConnection connect;
kern_return_t result;
IOSurfaceRef screenSurface = NULL;

io_service_t framebufferService = IOServiceGetMatchingService(kIOMasterPortDefault, IOServiceMatching("AppleH1CLCD"));
if(!framebufferService)
    framebufferService = IOServiceGetMatchingService(kIOMasterPortDefault, IOServiceMatching("AppleM2CLCD"));
if(!framebufferService)
    framebufferService = IOServiceGetMatchingService(kIOMasterPortDefault, IOServiceMatching("AppleCLCD"));

result = IOMobileFramebufferOpen(framebufferService, mach_task_self(), 0, &connect);

result = IOMobileFramebufferGetLayerDefaultSurface(connect, 0, (CoreSurfaceBufferRef*)&screenSurface);

uint32_t aseed;
IOSurfaceLock(screenSurface, kIOSurfaceLockReadOnly, &aseed);
uint32_t width = IOSurfaceGetWidth(screenSurface);
uint32_t height = IOSurfaceGetHeight(screenSurface);

CFMutableDictionaryRef dict;
int pitch = width*4, size = width*height*4;
int bPE=4;
char pixelFormat[4] = {'A','R','G','B'};
dict = CFDictionaryCreateMutable(kCFAllocatorDefault, 0, &kCFTypeDictionaryKeyCallBacks, &kCFTypeDictionaryValueCallBacks);
CFDictionarySetValue(dict, kIOSurfaceIsGlobal, kCFBooleanTrue);
CFDictionarySetValue(dict, kIOSurfaceBytesPerRow, CFNumberCreate(kCFAllocatorDefault, kCFNumberSInt32Type, &pitch));
CFDictionarySetValue(dict, kIOSurfaceBytesPerElement, CFNumberCreate(kCFAllocatorDefault, kCFNumberSInt32Type, &bPE));
CFDictionarySetValue(dict, kIOSurfaceWidth, CFNumberCreate(kCFAllocatorDefault, kCFNumberSInt32Type, &width));
CFDictionarySetValue(dict, kIOSurfaceHeight, CFNumberCreate(kCFAllocatorDefault, kCFNumberSInt32Type, &height));
CFDictionarySetValue(dict, kIOSurfacePixelFormat, CFNumberCreate(kCFAllocatorDefault, kCFNumberSInt32Type, pixelFormat));
CFDictionarySetValue(dict, kIOSurfaceAllocSize, CFNumberCreate(kCFAllocatorDefault, kCFNumberSInt32Type, &size));

IOSurfaceRef destSurf = IOSurfaceCreate(dict);

IOSurfaceAcceleratorRef outAcc;
IOSurfaceAcceleratorCreate(NULL, 0, &outAcc);

IOSurfaceAcceleratorTransferSurface(outAcc, screenSurface, destSurf, dict, NULL);

IOSurfaceUnlock(screenSurface, kIOSurfaceLockReadOnly, &aseed);
CFRelease(outAcc);

CGDataProviderRef provider = CGDataProviderCreateWithData(NULL, IOSurfaceGetBaseAddress(destSurf), (width * height * 4), NULL);
CGImageRef cgImage=CGImageCreate(width, height, 8,
                                 8*4, IOSurfaceGetBytesPerRow(destSurf),
                                 CGColorSpaceCreateDeviceRGB(), kCGImageAlphaNoneSkipFirst |kCGBitmapByteOrder32Little,
                                 provider, NULL,
                                 YES, kCGRenderingIntentDefault);
UIImage *img = [UIImage imageWithCGImage:cgImage];
saveImage(img);

I combined the code from IOSurface - IOS Private API - Capture screenshot in background and IOSurfaces - Artefacts in video and unable to grab video surfaces with little modification, the code works well in homescreen and most apps, but returns a black screen in games. Any ideas how to fix that? Thanks.