MUST READ: Lifted from a comment elsewhere:

What all skeptics do not notice is the fact that a forger only fakes something either preexisting or something which is known throughout the history. He never will fake something which was invented by him, because this is nonsense at all. Both conditions are not satisfied in the case of the Shroud of Turin, because neither the New Testament nor the apocryphal writings mention a single line about the existence of a cloth with the dorsal and frontal images of Jesus’ body. Christian tradition, on the contrary, mentions a cloth with only Jesus’ face (the Veronica veil). Before the Middle Age, nothing is mentioned about it, as well. Why will a supposed forger be at the same time so skilled in order to make such an astonishing masterpiece (which even today is very difficult-if not impossible- to copy) and so silly in order to ‘fake’ something unknown at his time?