pixel hunting

In video games, Pixel Hunting is usually referred to in point and click games as an instance where, while searching for a specific key object, the player must methodically click every single pixel on the screen to find the one which has said item. This happens when there is no visual cue about where it is, so all a player can do is click everywhere until he or she happens to find it.
Genereally discouraged in game design, as it makes the game artificially more tedious (and in a cheap way) than it needs to be.

Some call "The Witness" a pixel hunting game because you usually need to be clicking everywhere to discover the places from where you can solve the puzzles.