he is not the first and won’t be the last to demonstrate ways an image could have been produced using technology available in the middle ages, but nowhere does it state he tested the image and found evidence that his proposed method was used.
big deal, he is selling a book
“could have happened this way” does not equal “it is proven beyond shadow of a doubt that it did happen this way”
my personal opinion is and always has been that this image is of early medieval origin and like any other man-made religious image of the Lord that inspires pious reflection on His Life and Mission, it can be a valuable aid for the spirituality of the individual Christian. My opinion, like that of the claimant, is not fact and he has no more proof than I do for my opinion.