The Shroud proves nothing, either way.
If it is a medieval forgery, it is a fraud. If it does date back to the 1st century, that still doesn't prove it's Jesus. It just proves it is some guy who got crucified. There was no shortage of them in those days.
"Jesus, why'd you pick such a backward time and nation?
Israel in 4 BC had no mass communication.
Don't get me wrong, don't get me wrong, I wanna know, I wanna know..."
--Judas' song, "Jesus Christ, Superstar"