I'm wondering what other images will become illegal because they elicit violence...

In Germany (bastion of free speech that it is), any speech that is "capable of disturbing the public peace" is forbidden. Insulting someone is also prohibited by law. You also can't insult the "organs and representatives of foreign states" (so no talking about Dick's you-know-what). You also may not insult any faith.

For other restrictions, see here:

http://en.wikipedia.org/wiki/Freedom_of_speech_by_country