In this article The Mirrors Behind Rembrandt’s Self-Portraits Francis O’Neill, an artist and art teacher from England, suggests that Rembrandt used mirrors to project his images on the canvas to facilitate his drawing technique.

I find this suggestion very much improbable.  Rembrandt was not only a great artist but a marvelous painter, and to accuse him of “cheating” in such a basic skill  like drawing is comic.  It is interesting that the “accuser” is an artist himself, which leads me to conclude that because he, himself, cannot do what Rembrandt did effortlessly, gave in to the temptation to assume that somehow this great Old Master had cheated.