Well, it is of course barbaric to attack somebody that gives a lecture at a University. People that do this are criminals. There is never an excuse for this. A discussion of the topic is always warranted. But on the other hand, I would not myself hold a lecture at a University with pornographic images. It represents bad taste.
Whether or not there is a prophet on display at the same time is not so important. The dog with a prophet head is a better example if you want to discuss the religious problem. I'm one of those that claim that it should be possible to paint such a dog without getting death threats. Again, death threats are illegal. However, at the same time I don't think blasphemy, in general, is a good idea and something one should refrain from in respect for religious people.
I don't think there should be a law against blasphemy, though. As a religious humanist, ie, a pantheist that think God is Nature and science the means of searching for God, I don't think there should be a law against creationism or atheism. Because some people happen to believe in this fasion from their nature. In other words, bad taste cannot be made illegal.
It could of course be discussed whether the pornography was art. Someone said, how do you define pornography--I know it when I see it. So, if there are people in the audience that think it is pornography, it probably is.