“My Wife and My Mother-in-Law” by British cartoonist William Ely Hill is a famous ambiguous image, which can be perceived either as a young girl or an old woman (the “wife” and the “mother-in-law“, respectively).
Supposedly, if you’re young, you see the wife and if you’re old, you see the mother-in-law. It took me over half an hour to see the mother-in-law.
Here’s a hint. Cover the wife’s hat and hair with your fingers and the mother-in-law is revealed.
A Tiny Kitten With A Big Mouth
P.S. The other picture like this a now a book entitle, DuckRabitt. My nephew loves it.