Pareidolia

Pareidolia is a phenomenon where the mind assigns meaning to a random sound or image and responds to it by perceiving a meaning, even where none actually exists.

For example, seeing the image of the "man in the moon" or the face on Mars are examples of the mind assigning a recognizable image to a natural feature. In psychology, pareidolia can be seen in the usage of projective tests such as the Rorschach inkblot test (hyperlink?) in which therapists use patients' interpretations of ambiguous stimuli to glean insight into their mental state.