|The original image taken by the Viking 1 orbiter in 1976.|
Humans have always projected their own hopes and fears onto interstaller objects like this famous cultural anthropomorphism. As a social species we are particularly hard-wired to recognise faces. Perhaps this is the reason why Jesus pops up on a piece of toast, or a giant face emerges out from the shadows of arbitrarily arranged Mars rocks.
ESA/DLR/FU Berlin (G. Neukum), MOC (Malin Space Science Systems)(2006)
NASA used the likeness to their advantage, as a way to garner interest in Mars. They even suggested themselves in the 1976 press release: "The picture shows eroded mesa-like landforms. The huge rock formation in the center, which resembles a human head, is formed by shadows giving the illusion of eyes, nose and mouth." When NASA returned to Mars in 1997, they felt they owed it to the taxpayer and reshot this famous image. With better quality equipment, the mystery disappears. No human head, no alien monument. Just a natural landform.
Read more about unmasking the face on Mars.