Every time I move the camera focus, the fog of war flickers like mad. I've tried fiddling with in-game options, I tried running the game in compatibility mode for XP SP2/3 (I run Windows 7 64) and I installed the fix found at http://www.shsforums.net/topic/48732-ddraw-fix-for-slowdownsstuttering but I still get the flickering. I'm also running the widescreen fix, though I'm not sure which specific one because I installed this game a number of months ago.

There was another topic that mentioned using the Microsoft Compatibility Admin tool, which I also tried. Still no success. I'm tearing my hair out here, what the hell is wrong with this game?

the checker board pattern that fog-of-war uses causes problems.

load up a image of a small checker board pattern on your web browser and scroll the page, the pattern will flicker ( the widescreen mod forums are currently down, else I'd point you to an example )

the ddrawfix can cause some screen tearing ( uninstall that mod if you wish )

this is interesting
http://www.lagom.nl/lcd-test/inversion.php

your best option is to lower the resolution that your using with the widescreen mod

Thanks to the info on this page, I was able to fix the issue for my system:

My monitor (Samsung) has a setting called "Sharpness", which I had previously set to 60. Lowering it to 40 caused the fog of war to stop flickering. Play around with your monitor settings and see if you can find something similar.

(I'm aware the thread is ancient, but it's one of the first google results for that issue, so it can't hurt to have a possible workaround in here)

Another better option that only messes with sharpness in motion can be adjusting your LCD's overdrive setting. Annoying thing is that monitor manufacturers call it different things and not all of them has one.

aqrit also made a improved fog-of-war mod that was sadly never finished:
http://bitpatch.com/pstfog.html
Might be worth a shot if the other options don't work too well for you though.