As a quick note, after I'd written the post below, I noted that Charlie Hebdo has published modern cartoons illustrating the life of the Prophet. I believe in Freedom of Speech, but I also do not believe in needlessly insulting another religious and peoples' religious beliefs.
Whilst I am happy to post and discuss pre-20th century images of the Prophet Mohammed, I prefer to stick to images created by Muslim artists of their Prophet. There were thousands of images of him created by both Sunni and Shiite artists, and most Muslims I've discussed them with - from academics to taxi drivers - have had no issue with me discussing them in a historical context ... such is the climate of fear that when I discussed writing a book about them with a former agent I was told the publisher was only willing to publish a text-only book (kinda defeats the point of an art history book ...).
I will not be posting modern images created in anger, and I have avoided discussing the Medieval and Renaissance anti-Muslim images created by Christian artists.