1) Select your screenshot.
2) Import picture as plane for correct proportion.
3) Assign material "1920x1080"
4)
Change path to your screenshot picture in texture
"1920x1080" settings.
5) Select texture "monitor grid".
6) Set "size" in panel "mapping": resolution your picture = X and Y size.
7) Move camera.
8) Press F12
Sorry fo bad english ^___^
Very interesting shading technique, nice work! :)