What is the word for an image hidden inside a painting?

My father-in-law has a painting by Vu Cao Dam of two girls and a man on horseback. He found a hidden fox in the painting, and today we were looking at it and found some more.

What do you call it when an artist intentionally puts a hidden image within a larger work of art? My father-in-law swears there is a word, and that it is a general term which can apply to different media. It can apply to actors who make cameos or easter eggs in software.

What word is this?

Solution 1:

As per snubian I suggest steganograph.

Solution 2:

The term anamorphosis seems to be close – it describes a type of concealed image that requires viewing either through/with a special device, or from a particular perspective, in order to reveal a feature or shape that is not immediately apparent to the casual observer.

I have also discovered that 2D optical illusions bearing hidden 3D projections that your brain can be tricked into seeing, (Magic Eye-type images), are called autostereograms.

Solution 3:

I would call it a hidden, double, multiple, or ambiguous image; or, if the hidden image were especially non-sequitorial, perhaps "a shining example of the paranoiac-critical method". Some hidden images are due to the Figure-Ground phenomenon, others are due to Gestalt, others I'm sure are due to other things. Other than "easter egg", though, I can't really think of another alternative. Perhaps the links will have something I missed.

P.s. Dali's The Endless Enigma is the best example of multiple hidden or ambiguous images that I know of.