In 1531, the Virgin Mary appeared to Mexican peasant Juan Diego. To prove to all that the apparitions were real, the Virgin imprinted an image of herself on Juan Diego's tilma, a thin cloth made of cactus fibres. This type of tilma normally decays in 30 to 40 years. But Juan Diego's tilma is still miraculously intact and the same as it was when he wore it. Over the centuries, many have expressed doubts about the divinity of the image, but Prof. Victor Campa Mendoza has no doubt whatsoever. "This is not a human act but an act of God,"...