iOS
takes screenshot before your application goes to background.
I got it from Apple's official documentation.
Remove sensitive information from views before moving to the background: When an app transitions to the background, the system takes a snapshot of the app’s main window, which it then presents briefly when transitioning your app back to the foreground. Before returning from your applicationDidEnterBackground: method, you should hide or obscure passwords and other sensitive personal information that might be captured as part of the snapshot.
So, Here We can hide our "sensitive personal information" and the system takes a snapshot of the app’s main window and we are not able to change its feature.
# sensitive personal information
Set a blurry screen overlay before the app goes in the background and once the app becomes active remove this overlay (check @cweinberger's answer).
If it is
iOS 7
or later you can use the functionignoreSnapshotOnNextApplicationLaunch
Also,allowScreenShot
flag can be explored in Restrictions Payload.
For deeply read about it Then this is the best documentation.