I just love words and this is one I have been trying to remember. It describes the experience of seeing a recognizable object as a distinct and recognizable image. For example, the face of Jesus in a burnt tortilla, or the face of Mary on a grilled cheese sandwich. (There's money in this stuff. The toast sold for $28,000 despite its being a little stale.)
A related word is apophenia. It has a slightly different meaning and is a recently created word (1958) "The propensity to see connections between seemingly unrelated objects or ideas most closely links psychosis to creativity ... apophenia and creativity may even be seen as two sides of the same coin."
Wow your friends the next time they see Pope Benedict in a mashed potato by describing their experience as a pareidoliac phenomenon. :)