BBC BASIC Programmers' Reference

by Richard Russell, November 2014

Suppose your program displays something which you would prefer the user not to be able to capture in a screenshot (e.g. using the Print Screen key). You can do that as follows:

        WDA_MONITOR = 1
        SYS "SetWindowDisplayAffinity", @hwnd%, WDA_MONITOR

Once this code has been executed, the specified window (here the main output window) will appear black in a screenshot.

Of course you can't stop the user taking a photograph of the screen, but the above code will go some way to discouraging the capture of your program's output