Today's Image of Mohammed shows him converting, which he was far better at than Jesus Christ, I must admit. Christianity began to take off after the Crucifixion, but Islam had begun its journey to become one of the dominant religions within Mohammed's lifetime. Although Mohammed was one of the great generals of his age, he did not force conversions by the sword, and told his followers not to either. He felt that conversion should come as a result of preaching, which he is shown doing in this image. The face of the congregation (click here for a larger image: BNF) are notable for their diverse features and ethnicities, and show how Islam unified a variety of peoples through religion.
Mohammed is in the pulpit, and a lamp hangs to the left of him, showing that he is in a mosque teaching the Word of Allah. He, like those he is teaching, has a halo and his face is clearly visible. Persian, 1489, BNF.
The Mohammed Image Archive points out several almost identical depictions of this popular scene, with Mohammed's face visible: here, and here. The plethora of images of this scene show the great importance placed by Islam on voluntary conversion - modern 'conversion by the sword' of terrorist groups would have been frowned on by Mohammed. And yes, I have read the Koran (and some Sharia).