How to fix stretched image [Widescreen fix] (Dark Sector)

In the game options put the permission you need. Suppose 1920x1080. Save and exit.

Open Notepad DS.cfg in the Dark Sector\Configs

On the next line after this [Windows_Config,/Types/Config] add this line:
Graphics.DisplayAspectRatio=FullScreen4x3
Yes, write it 4x3 despite the fact that you have a widescreen display. It must be so.

Save DS.cfg. Go into file properties and set the attributes checkbox read Only. Is that the game does not rewrite the file.

And voila! You have a neat picture for your monitor format without distorted proportions.