Pareidolia

Pareidolia is where you look at some form that is vague and random (like a cloud) and see something in it (like a face). There's a more precise description in the Skeptic's Dictionary and it's also mentioned is this week's James Randi newsletter.

So looking at the Nun Bun and seeing Mother Theresa is an example of pareidolia.

This one's something similar with a blurred picture taken from a Spanish website.

The famous face on Mars.

The Pittsburgh Ghost Hunter's site has a warning for ghost-hunters about pareidolia; although they seem to have ignored their own advice when it came to the Curtain Face image - in fact check out the rest of their gallery for some very unspooky pictures - ooh, is that a ghostly orb or just a fleck of dust on the lens or in the air?