Greg F, thank you for the link. I haven't read it all :) However, what I have read is interesting.

A person when first charged with a crime is entitled to a presumption of innocence, and may insist that his guilt be established beyond a reasonable doubt. However, it was observed that [d]ue process does not require that every conceivable step be taken, at whatever cost, to eliminate the possibility of convicting an innocent person.

Once a defendant has been afforded a fair trial and convicted of the offense for which he was charged, the presumption of innocence disappears and there is a lot in the link which highlights the difficulties that someone, who has been wrongly convicted, faces to clear their name once that presumption of innocence disappears.