Muslim rage and loopholes

On the topic of extremist Islam and Danish cartoonists, one thing that's just occurred to me, and has me wondering, is this:

If Islamic law strictly forbids any representation of the Prophet Muhammad, then how does anybody know what he looks like? And if nobody knows what he looks like, then how can you recognize him in a cartoon then break into rage? I mean, since it's forbidden, I assume there has been no proliferation of his image over the years, so how does anybody know what he looks like? Or are Muhammad pictures smuggled around like a teenager with a Playboy magazine? "Mehrdad, what are you doing in there?" Nothing Mom, nothing! (I'm just looking at Muhammad)

And, don't Muslims know when people are taking the piss out of them? I mean, does Islam not allow for humour? I mean, if I said "I know exactly how you will react to the following: You are going to flip out and declare Jihad. Look at this. " Guy flips out, first shouting, then finger waving, declares Jihad, etc. If I had any pride, I wouldn't allow someone to take the piss out of me like that and manipulate me like a marionette.

In the end, the cartoon was a stroke of genius. Depict a group of people as a bunch of bomb-wielding lunatics, and upon seeing such a prophecy, they all turn into a bunch of bomb-wielding lunatics in protest. Better irony gibt es nicht.

But I said it before, Muslims are always about 400-600 years behind the Christians, so they haven't had their reformation yet, and Christians were uniquely brutal in their beliefs, as Christianity at that time had very little to do with God's love and more to do with Men's power over things.