There is one justification to support the authenticity of the Shroud that I have never seen put forward ... the wounds on his head that line up with the crown of thorns. There were many crucifixions at that time but how many of these victims were given a crown of thorns to wear. The crown was given in mockery of our Lord's testimony to His heavenly kingdom. For non believers, those wounds stand as testimony to the only one history records as having been given a crown of thorns.
This is also one of the main things that skeptics use to point out that it is a fake produced by the hand of man.
They say that the crown of thorns being included is proof that someone "painted" it. Why else would they include it other than to get the masses to believe it is an image of Jesus?