I think that the infobox should at least have a picture of Muhammad, if there is to be one anywhere.  The image for the page on Muhammad should be a depiction of Muhammad.  Having calligraphy or symbolism replace an actual picture would not be in the spirit of wikipedia.  Regrettably, it will offend some people, but that is not, nor should be, the impetus behind any decision.  A picture of Muhammad would be more encyclopedic and offer more knowledge, therefore, it is the only real option if this is to remain a truly neutral place to obtain knowledge.  Also, I feel like there is an overabundance of images in this article.  Lots of images of redundant or mildly irrelevant things, as if people are unconsciously putting in different images because they feel bad about putting in an image of Muhammad.