The most compelling evidence for me that the Shroud is authentic is the Bible. We know there is a Shroud and a Head covering. We know the head covering was kept as a holy relic. So why wouldn't they also revere the Shroud as well? No one is going to keep the head covering as a sacred object of the Lord but throw away the Shroud. So then, where is the Shroud? Either the Shroud is real or it is a forgery of the real thing. But if it is a forgery the easiest way to prove that is to bring out the real one. If Satan has been unable to destroy the Bible, the word of God, then it is absurd to think that he can destroy the Shroud. I personally believe that God left behind the Shroud and the head covering because He knew that some, like doubting Thomas, need physical evidence of the resurrection. The head covering is essential because it has the same blood type as the Shroud, the odds of that are 1/10. That is a powerful testimony that it is authentic. According to the Bible you need two witnesses, but this one witness is very powerful. Likewise the physical evidence on the Shroud is equally compelling. The two witnesses alone easily make the odds of it being real well over 99/100.