A shadowy image in a strangely shaped frame, like flames turned upside-down. Looking closely, one can distinguish a face, elongated in the Medieval style, darkened by centuries of old varnish and incense smoke. This is the Holy Mandylion, the True Image of the Holy Face, a nearly forgotten remnant of the Iconoclast debate c.600-800 CE.
On one hand, it was well-nigh imperative, in a world before widespread literacy, to have a visual component to Christianity, especially if it was to unify common people and the Roman Empire. On the other hand, the commandment not to worship graven images was clear, and the Jewish tradition did very well without them.
The Mandylion, or holy towel, "an image not made by hands" was a cloth given to the court painter Ananias of Abgar V of Edessa (now in Turkey, then part of Syria) from the hand of Jesus Himself, which miraculously had become imprinted with a perfect image of His Holy Face. The story went that the King had been suffering with an unspecified ailment (gout or leprosy, depending on the source), and had heard of a preacher/healer in nearby Judea who could help. He thereupon wrote Jesus a letter, and sent it by way of the same Ananias, who was charged with returning either with Jesus or an image of Him. Upon seeing The Son of God, he was so struck by his radiance that he was unable to paint him, and could hardly hand him the letter. JC, being both literate and courteous, read the letter, drafted a reply (some say dictated) remarking that he was very busy at the time, but would be happy to send an apostle (St. Jude Thaddeus) to look into the matter. Then, wetting his face, he toweled off, and presented the towel "as consolation for his illness". Working from the image left on the towel either by miracle or by dust, Ananais was able to reconstruct a suitable image for his King, who was deeply touched, and put the towel away in a safe place.
The towel in question then had a rocky history. It was hidden behind a tile to ward off a Persian invasion, and mysteriously caused the tile to bear the same image. It was shown to duplicate itself. Little is certain except that it reappeared in the 600's at the height of the pro/anti icon debate, and appeared to settle the matter clearly on the side of images. The image itself became the property of the Emperor of Constantinople, and remained so until the Sack of Constantinople in 1204. From there, it passed to the French Royalty, who enshrined it at Sainte-Chappelle, in Paris. Or did they? Two other contenders for the Mandylion turned up in Genoa and in Rome, and copies were popular in Russia, where theologically, they were placed in the same category as the Eucharist as the literal Body of Christ. The Parisian Mandylion disappeared during the French Revolution and is probably permanently lost.
Are the other two real? Probably not. Of the remaining two, only the Roman Mandylion (now in the Pope's private chapel) incorporates actual linen cloth into the image. This face, if it was ever really imprinted onto the cloth, has been painted over several times, according to the Vatican's own restoration department, and is, as I've alluded before, not in a style consistent with 1st century Syria. Neither is the face recognizably of a Judean peasant of that era, being more like a Byzantine Imperial court portrait. Some people have attempted to identify the Mandylion as the Shroud of Turin, but evidence is scanty.
More importantly, perhaps, is the significance the Mandylion has had to Western art. Prior to its veneration, Christian iconography and secular portraiture seemed on the same track as that of contemporaneous Islam. Few permanent paintings (that is, not intended as banners, or other ephemerata) were ever done on cloth. By proving that Christian faith and figurative art could coexist, a pious fraud ensured we now have the vibrant range of images we have today. It seems like a small price to pay.