The goal of a satirical art hoax is to call into question the judgement of art critics. The hoax involves presenting a critic with a work for evaluation. If the critic determines that the piece displays talent and skill, the hoaxer then reveals that the work actually came from an unexpected source that couldn't have had such skill. For instance, it might have been the work of an animal such as a donkey or chimpanzee. Or a six-year-old child. Or perhaps the hoaxer himself created it, having purposefully made it as bad as possible. Whatever the case may be, the implication is that the critic is a fraud, unable to discern true ability.
This type of hoax became popular in the early 20th century, as art became increasingly abstract, leading to a growing gap between what leading art critics were labeling as worthy art, and the older, more traditional concept of what art should be. Similar hoaxes began occurring in literature (particularly poetry) at the same time.
However, these satirical art hoaxes draw upon a much older tradition (dating back well into the Middle Ages) of mocking academics and intellectuals who have spent so much time in their ivory tower that they've lost touch with the everyday world. In this way, these satires tell an appealing, timeless story about the superiority of the common sense of regular folk over the judgement of the learned and supposedly wise.
Sneaking Into Museums
A variant of the satirical art hoax involves a hoaxer sneaking one of his own works into a museum and hanging it on the wall. If the museum directors don't immediately notice it as being out of place, this implicitly suggests that they accepted it as worthy of being in the museum. Again, this calls into question their standards of judgement because under normal circumstances, knowing the true authorship of the work, they would not have allowed the work in the museum, but when its already there, they assume it belongs.
Le Bateau (right-side up)
A phenomenon that's closely related to satirical art hoaxes, in that it's perceived as demonstrating the hollowness of art criticism, is the history of art shows mistakenly displaying artworks upside-down. Famous examples of this include The Fossil Hunters
by Edwin Dickinson (accidentally hung sideways when exhibited in 1928), Pink Lilies
by Margaret Gest (which won a prize in 1936 despite being displayed upside-down), and Le Bateau
by Henri Matisse (accidentally hung upside-down for 47 days in 1947 at the Museum of Modern Art). The Apesheet
website lists even more examples of this phenomenon.