Then why is it there? What actual purpose does it fill?
To show this particular general/religious leader has been historically depicted.
We don't even mention that say the image in Pope Linus is somewhat unlikely to be historically accurate (the history of the early popes is somewhat historically problematicalical). Saul of Tarsus would be another one who throws up this issue.
-- geni
But historically images of Muhammed have been strongly discouraged, generally, he has not been depicted. Examples from Christianity and Europe are not to the point. Christian culture has not focused on this issue while Muslim culture has (at most times and places). Images of Mary and Jesus are common. That they bear little or no relationship to the historical figures is generally not an issue. A phony image of the Prophet of Islam is.
Fred