Fooled by depth
Trompe-l’œil
Is the boy climbing out of a real frame?
No: the frame is painted too.
Why? “Trompe-l’œil” is French for “deceive the eye.” Painters copy the light and shadows of real things so carefully that your brain takes them for real. This one, by Pere Borrell del Caso, is from 1874.
Picture: Elke Wetzig ( User:Elya ), Public domain · Wikipedia(opens in a new tab)