[pacbard]

The difference between a super GM and stockfish is that a super GM will play moves the "feel natural" to a human given the current position on the board. A chess engine won't care about what is natural and will maximize the position 15-20 positions down the line. For this reason, they will make sometimes a weird move given the current position that will result in an advantage a lot of moves downstream.

One of the main reasons that Petrosian "got caught" was other GMs (see Hikaru's YouTube video on this) pointing out how unnatural some of his moves felt to them and considering the speed at which he supposedly calculated them.

[pashamur]

That is true of traditional chess engines, but no longer true for neural net (self-taught) engines that learn the rules of chess by simulating millions of games against itself.

I've played an early version of one of those (its playing strength is roughly proportional to the amount of training it has done) and it was quite human-like in its behavior, even dropping pieces and making very human-like mistakes.

Look up AlphaZero and the open source port LeelaChess :) Once those become commercially available, it's going to be very hard to detect engine usage.