[ajwar]

1. Would it be possible to force player press screenshot (f with some kind a plugin?

2. Is it possible to check if player using f12 button?

[reckst4r]

It is impossible to force a player to take a screenshot, and I'm pretty sure that it's impossible to check if a player is using f12.

[]Rafaellos[]

By pressing F12 you mean to enable/disable the s0.beit? I had the same idea but s0.beit users can change their enable/disable button with something else.

There are some ways to detect if player is cheating, but no all of kings of cheat. Try search for an anti-cheat script.