This is gonna get you mad.
I was browsing my screenshots from the Half Life 2 mod "The Hidden"...a game where you play as member of a squad named IRIS...the objective is neutralize the subject 617. The bad thing is that this guy is invisible, except some water effect if there is some light in the room. So...somewhere in this screenshot the is the hidden

find it and you will win 50k, use Paint to mark the area with the pencil tool.
This is the screenshot