Impossible Elephant Illusion was created by a scientist named Roger N Shepard, and first published in 1990 on page 79 of his book Mind Sights. He gave it the name "L'egs-istential quandary." It is based on a dream he had in 1974. When he woke up from the dream, he made a pencil sketch of the elephant, which he later turned into a pen and ink drawing for his 1990 collection of paradoxical images and illusions.
Shepard's elephant iis an example of an "impossible image" of the type "figure-ground illusion." That is, the artist intentionally confuses you between the figure and the background.
The image has been widely distributed without attribution to Shepard. An anonymous user on 4Chan's /x/ board made the poster into a public domain image and it caught on as an optical illusion.
- Illusion Elephant Illusion