a game screenshot is always possible with printkey or other tools
or by operation system with hardware keys.
if you want compare who is best by a screenshot maybe
save the screenshot within agk and add a watermark or something
that other can not reproduce with photoshop.
or did you mean printscreen give the user more time at playing?
this would result in a different GetFrameTime () or can detect with Timer()
AGK 108 (B)19 + AppGameKit (Steam) V2 Beta .. : Windows 8.1 Pro 64 Bit : AMD Radeon R7 265 : Mac mini OS X 10.10 (Yosemite)