Regarding this question, it seems that print screen ( either by Home + Sleep or via Assistive Touch menu ) cannot be prevented without using iPhone Configuration Utility.
But in this article, it suggests that iOS 7 ( starting from beta 4 ) has a new API to detect screenshot. I tried to look into Apple's iOS 7 documentation but it does not directly mention anything related.
Is the new API available in iOS 7 ( official version ) ?
It is possible to detect screenshot by a new method in UIApplication class, called UIApplicationUserDidTakeScreenshotNotification.
Notification will be posted when user presses Home + Sleep to print screen. Available in iOS 7 or above.
Reference: UIApplicationUserDidTakeScreenshotNotification docs