The role of the dealer in visual cryptography
The dealer is one of n participants or it should be from outside?


The dealer, knows the secret as he's the one who shared it. Thereby it makes no sense to give him a share as well, unless you have a such a scheme that requires all partys to collaborate to recover the image, but then the question becomes: "Why bother secret sharing at all if the dealer could just store it if consensus with him is required?"

TL;DR: He can be part of the participants, but there's no benefit of him being one.