The spreading Muslim protests against newspapers that reprinted cartoons depicting the Prophet Muhammad stem from the deepest religious roots.
Islam forbids visual depictions of the prophet, and regards violations by Muslims as highly sinful and by non-Muslims as the ultimate sort of insult.
The prohibition is in part an application of the Quran's strict opposition to idolatry, the worship of a physical object as a god, including any hint of such devotion toward the faith's revered human prophet.
In the Quran, "shirk" (Arabic for "partnering" or "associating" anything with God) is the one unforgivable sin: "God does not forgive the joining of partners with him: anything less than that he forgives to whoever he will, but anyone who joins partners with God is lying and committing a tremendous sin" (4:48).
The Quran does not specifically address artwork of Muhammad, and through history a few Muslims have painted him. But the ban has been virtually universal in all branches of the faith from its earliest days.
The rule extends to artwork showing others regarded as prophets by Islam, including Jesus, even though Christians have often visualized their divine savior in paintings, statutes and films.
Muslims disagree among themselves on whether it's proper to portray the prophet's early followers, known as the Companions. Unlike Sunnis, Shia Muslims allow images of their greatest saint, Ali, Muhammad's son-in-law.
Some Muslims oppose any art that depicts humans, and Muslims have tended to specialize in nature paintings, decorative arts and calligraphy. Some were wary of photography, too. But Zahik Bukhari, director of Georgetown University's American Muslim Studies Program, says those attitudes are fading.
A second aspect of the depiction ban is noted by John Esposito, editor of "The Oxford Encyclopedia of the Modern Islamic World." Besides shunning any hint of idolatry, he says, the practice also expresses "the deep reverence and respect Muslims have for Muhammad" as "the ideal Muslim." He notes that when the prophet is named, believers always add "peace and blessings be upon him" and that he is sometimes called "the living Quran."
Bukhari says the cartoons, first published in Denmark, constitute a triple offense for Muslims: first by depicting Muhammad at all; second by treating him disrespectfully; and third because "in the present circumstance it is a symbol of the clash of civilizations that they want to insult the prophet and the whole of Islam."
Esposito, who is Roman Catholic, says the ban is so important that, for Muslims, the cartoons reinforce "a deep-seated belief that respect for Islam doesn't exist" in Europe.
"It can be read as a deliberate attempt to provoke and test, not only religiously," he said. "It expresses the tensions toward immigrant communities. It says this is what democracy is about: nothing is sacred."
Sayyid M. Syeed, secretary general of the Islamic Society of North America, said it's important that non-Muslims distinguish between freedom of opinion on religious matters and needless offense.
Muslims respect free speech rights, Syeed said. But "in a democratic environment, living in a pluralistic society, people should know they have to respect the sensitivity of Muslims on this issue. It does not muzzle their freedom of speech in rejecting Muhammad as the prophet."