Here's what encarta says, I'm quoting encarta because it's pretty much an anti-religion, anti-God program. The advisory board is full of atheists.
So, they're quite unfair, yet the following is very unusual I must say, i thought the debate was pretty much over and it had been declared a painting, no, no, they don't know how the image was created and carbon-dating is unreliable.
Turin Shroud, length of linen cloth which has been venerated for centuries by some Christians as the burial garment of Jesus Christ.
The shroud shows an image, resembling a photographic negative, of the front and back views of a man, just under 2 m (6 ft) tall, and displaying marks which allegedly correspond to the injuries suffered by Jesus as described in the Gospels. These include thorn marks on the head and lacerations on the back.
The existence of a strikingly similar cloth, the Mandylion, was recorded as early as ad 500, though the cloth was lost after the sack of Constantinople in 1204. The first certain records of the Turin Shroud date back to 1354, when it was in the possession of a French nobleman, Geoffrey de Charny. In 1453 it passed into the hands of an Italian family, the Savoys, who kept it for some years in Chambéry, France, where it was damaged in a fire. Finally, the shroud was taken to Turin Cathedral, where it has been preserved ever since, and exhibited publicly only on rare occasions.
Since the shroud first came to light, it has been the focus of controversy and debate regarding its authenticity. It has been the subject of experimentation since the late 19th century, as scientists have attempted, without conclusive results, to establish how the image was created. In 1988, the use of radiocarbon dating showed that the cloth had been made some time between 1260 and 1390. However, even radiocarbon dating (see Dating Methods: Radiometric Dating) is subject to uncertainties, and there is continuing dispute over the authenticity of the shroud. There are several conflicting theories concerning the techniques used to produce this remarkable image. It was suggested that the figure had been painted, but experts say that a medieval artist could never have produced that type of “negative” image. Many tests have been conducted to establish whether the image was produced with paints or other pigments, or even scorch marks. In 1978 a team of researchers found that there were human bloodstains on the cloth, and concluded that the markings on the shroud must somehow have been made by a human body. None of these experiments have given any conclusive proof, however, and the origin of the image is still a subject of much speculation.