First thing you should do to make this evidence acceptable is to turn on timestamp by pressing f11 key on your keyboard when Game window is active.
- Open game chat window as much as you can.
- Press Print Screen Button (PrntScrn, PtSc... etc)
- Open Windows Paint [It is installed by default on almost every Windows version] (You can use at this point any kind of image edition App, i.e: Gimp, Photoshop, etc)
- Paste the image (Ctrl+V) you just have recorded on your PC memory (Please keep in mind that if you press Print Screen Button several times, just last image you did capture will remain on your computer memory)
- Save image as .JPEG format