One screenshot into the clipboard should be possible with PrintScreenKey anyway, but you would have to ALT+TAB out of the game and load the clipboard into a program like Paint (comes with Windows) PAINT.NET or Gimp (both free) - or Photoshop or Paint Shop Pro.
(Even one of the old Photoshop versions comes free now)
http://getgreenshot.org/ could do the job for you - with d3d active.
There are more free screenshot tools on the internet. You just have to try/make sure, they process ingame shots.