CGImageSourceRef source = CGImageSourceCreateWithURL( (CFURLRef) aUrl, NULL);
CGImageSourceRef source = CGImageSourceCreateWithData( (CFDataRef) theData, NULL);
NSDictionary* metadata = (NSDictionary *)CFBridgingRelease(CGImageSourceCopyPropertiesAtIndex(source,0,NULL));
CFRelease(source);
Check the dictionary contents here.