This allows you to read a PNG image from "path" using Core Graphics functions and then access the bytes that back the image.

gistfile1.c

//path is a plain C string with the path to your image
CGDataProviderRef sourceDataProvider = CGDataProviderCreateWithFilename(path);
CGImageRef sourceImage = CGImageCreateWithPNGDataProvider(sourceDataProvider, 
                                                          NULL, 
                                                          NO, 
                                                          kCGRenderingIntentDefault);
CGDataProviderRelease(sourceDataProvider);
CGDataProviderRef sourceProvider = CGImageGetDataProvider(sourceImage);
size_t width = CGImageGetWidth(sourceImage);
size_t height = CGImageGetHeight(sourceImage);    
CFDataRef sourceData = CGDataProviderCopyData(sourceProvider); //Release this later
CFRelease(sourceImage);
CFIndex sourceBytesCount = CFDataGetLength(sourceData);
const UInt8 *sourceBytes = CFDataGetBytePtr(sourceData);