sense of the concept of TAWHID was so great and his humility so great, that he kept people from making images of himself. i certainly believe that had they made it a custom to make his image back then, they would have indeed worshipped him. contrary to his preaching to the oneness of ALLAH SWT. praise ALLAH SWT that we didn't fall into the practice of shirk like others have.
How do we (current time) draw the prophet muhammad, we don't even know how he looks like.