How to capture the screen of a window that contains transparency?

[salem c]

Cross-posted
https://docs.microsoft.com/en-us/answers/questions/702376/how-to-capture-the-screen-of-a-window-that-contain.html
https://stackoverflow.com/questions/70777503/how-to-capture-the-screen-of-a-window-that-contains-transparency

[seeplus]

Also asked and answer given at https://forums.codeguru.com/showthread.php?565690-How-to-capture-the-screen-of-a-window-that-contains-transparency