Somewhat easy to detect a human using a computer, by comparing to what the computer would do, the rating of the player and the usual play of the player. However

Somewhat easy to detect a human using a computer, by comparing to what the computer would do, the rating of the player and the usual play of the player. However, a chess professional would be able to use a chess computer almost undetected, as they know what would look like "computer moves", but could use it to just choose the best of their own suggested moves.