Doubts have been raised about whether Juan Diego existed due to the lack of contemporary accounts. However, these doubts were quashed, at least any reasonable doubts, in 1995 with the coming to light of the Codex Escalada which has been dated to the sixteenth century. It bears the date of 1548 and is an illustrated account of the apparition with text in Nahuatl describing the encounter between Juan Diego and Mary. The document bears the signature of Father Bernadino de Sahagun, a missionary priest and historian in Mexico, and a contemporary of Juan Diego. The first mention of the image in Spanish is in 1556 in a sermon preached by Archbishop Alonso de Montufar, the successor to Archbishop Zumarraga, in which he recommended devotion to the image. Devotion to Our Lady of Guadalupe spread rapidly throughout the Catholic world, with Genoese Admiral Giovanni Andrea Doria having a copy of the image on his flagship during the decisive Christian victory at the battle of Lepanto in 1571.
The image I believe is miraculous in nature. However, many spurious claims have been made about the image, and the video below is a good compilation of some of the wilder ones.
Not one of mine. :D