Illusionism and math always walked together with art. From Golden Ratio to Photoshop, we have uncountable examples in history when science helped the artists to "delude" the eyes and the brain, creating curious masterpieces. Anamorphosis (from Greek na+morphé, "no form") is one of these creations, purely based on manipulating the visual perspective -- at the same way we look at the traffic signals' paintings proportionally distorted on the ground.
It's a simple concept: a distorted image that, by observing a specific focal point or through a reflecting object, is seen as recomposed by our eyes. The first experiments of this technique goes back to the 15th century (began by Leonardo Da Vinci) and were used on several pictures, murals and frescos whose paintings were mingled with the architecture of the walls. "The Ambassadors", by Holbein, where a skull is revealed when observed from a determinate angle, is most know example of Anamorphosis of this period.
But the using mirrors technique, whose first registers goes back to Ancient China and was spread out on the 17th century, is certainly the most curious one. From that on, Anamorphosis left the artistical mark and became part of the popular taste, spread out in order to transmit political messages, caricatures and erotic images for those who knew the "secret" of the mirror.
The process was rediscovered by visual artists at the end of the last century, recognized again as a great potential artistic tool. One of the contemporary highlights are the works of the Hungarian István Orosz, compositions rich in details which link the anamorphic image as much as a resultant reflex.
Even with its exotic characteristics, Anamorphosis is highly present at the popular culture and in our daily life. Besides the mentioned traffic signals on the asphalt, we've got examples on posters, album covers, movies, advertisings and even beer brands which use this resource. The Kurt Wenner and Julian Beever's chalk art brings the anamorphic art literally to the streets with their tridimensional draws. In Brazil, who passed through the São Paulo metro station called República, could closely gaze upon the Antonio Peticov's "Anthropofagic Monument with Oswald de Andrade", a genuine example of Anamorphosis using mirrors and perspective. The art illusion, after all, isn't so far of the concrete and prosaic real world.