The above photo is a famous example of pareidolia. Pareidolia is the phenomenon in which unexpected images appear in some object. If you've ever laid in a field and identified the clouds as true images and shapes, then you've engaged in pareidolia. Famous examples in Texas relate to a pious Mexican grandmother finding the image of the Blessed Virgin Mary on a burned tortilla.
The famous photo above seems to show the face of Christ floating between a man and a woman. But look again...
...it's not Christ's face, but a young child. The "forehead" of what would be the face, is a white hat and the "nose" is the curved arm. The "eye" is the child's face and the "eyebrow" is the shadow under the hat. Do you see it? The child's hand is the "mustache" and the child's bare knee is the "chin."
Images like Saint Juan Diego's are clearly not examples of pareidolia. The same goes for the Holy Shroud of Turin. Some skeptics hold that so-called miraculous images are mere pareidolia, but clearly this is not mere pareidolia:
Our Lady of Guadalupe is clearly a miraculous image.