iPhone screen shots in background

Is it possible to take screenshots in the background? I was using UIGetScreenImage(), but in the console it outputs that your not allowed to take screenshots in the background. Any way to get this开发者_StackOverflow中文版 working without a jailbreak, I don't care if Apple will approve it or not, I just need it work without a jailbreak on the device. Thanks.

UI calls have to be on the main thread. Why can you not just do a UIGetScreenImage() call on the main thread?