I think I solved this issue. But my English is not very good. Read this English site and do that.

http://www.top-windows-tutorials.com/dep-settings/

After that not only the flickiring disappear but the graphics will improve a lot. The same with other very old games. After that turn off any compatibility modus. Just open as administrator and the graphic will improve even more.

To be really sure you should also save Torment in a Document folder not in C:\. Because there are certain security destriction by Windows. I actually dont understand why Gog installed in C:\. You should install in a Documents folder because there are no destrictions. In C:\ you cant even change an ini.file without annoying inconveniens.

I hoped I could help you.

I've found a way to fix it. However, it's not very convenient. You just have to shut down explorer.exe for the time of playing. You can do this in task manager (Ctrl+Shift+Esc). Just select explorer.exe and end its process. Warning: this will cause your desktop and taskbar to disappear until you start explorer.exe again. This is completely normal.

http://www.gog.com/forum/planescape_torment/flickering_2

In case that doesn't work (or introduces other problems, like slowdowns), you can also try DDrawCompat.

It seems that killing explorer works on Windows 8 and 10 as well. You can write a batch script, that automatically kills explorer, runs the game and after you quit the game, it restarts explorer for you.

Just open your notepad and copy/paste the following:

@echo off
taskkill /f /IM explorer.exe
Torment.exe
Start explorer.exe

name it wathever you want, but remember that it has to have .bat extension. E.g. torment.bat. Remove the automatically added .txt, and change it to bat. Then put the file in the torment main directory, make the shortcut on your desktop and start the game from it. For me it does its job pretty well :)

This works shockingly well. Thank you!