An unattributed drawing originally published 23 October 1892 in Fliegende Blätter, a German humour magazine. This is a trick picture adopted by Psychologist Ludwig Wittgenstein to illustrate seeing as. The drawing can be seen as a duck or as a rabbit, but not both at the same time. Such double images present two possibilities, but our mind must literally switch between them.
Berkeley's philosophical position that the essence is in the perception, if restated might be: we do not simply see, but always see as.