So that the crew would not have to use CGI to "fake" the magical illusions seen, Norton received intensive training in sleight of hand and other stage magic techniques from British magician James Freedman and American magician Ricky Jay.
Although the story is fictional, some details are based on the life of Austrian Crown Prince Rudolf, only son of Emperor Franz Josef. The painting Eisenheim creates is an actual portrait of Franz Josef. The bodies of Rudolf and his mistress, the Baroness Mary Vetsera, were found at his hunting lodge, Mayerling, on January 30, 1889, in what became known as the "Mayerling Incident". The Imperial Family covered it up at first, creating controversy and mystery.
The character of Eisenheim is closely based on magician and supposed clairvoyant Erik Jan Hanussen, who was famous in Vienna in the early 20th century. He was murdered by Nazi soldiers in 1933.
The Orange Tree trick was made famous by a 19th Century French magician named Robert-Houdin. It was from Robert-Houdin that another magician, Ehrich Weiss, came up with the stage name Houdini. This trick is first mentioned in old Indian manuscript as an illusion by Faux. Pinetti, an 18th century magician, did a similar trick, but he used lemons. Houdin was the first one to use real fruit.
The method for creating the ghosts as shown to inspector Uhl involved the projection of a pre-recorded image into a hazy background. Since the ghosts Eisenheim conjured could speak to and interact with the audience, he most likely used a different method popular among magicians at that time. A fantascope was used to illuminate a real person off stage. The image was reflected off of a mirror or glassplate, creating a ghosted image. The lanterns that Eisenheim tells his assistants to leave behind when they are packing up the workshop bear a strong resemblance to fantascopes.
Edward Norton did many of his own magic tricks, with the coaching of James Freedman. He worked with Norton preparing him for his stage performances and acted as a hand double in numerous situations.
The love scene was entirely lit by kerosene lamps. By the end of each take, the small room was so filled with smoke that it was hard to see.
When Sophie comes up on the stage during Eisenheim's show, she lifts the hem of her dress with one hand as she walks up the stairs. In the time this movie was set, a woman who lifted the hem of her dress with 2 hands was a prostitute.
When Inspector Uhl approaches Prince Leopold while hunting, to inform him of Eisenheim and Sophie's meetings, the Prince asks what they were seen doing together. The line asking if they were seen "fornicating" was originally filmed as "fucking." It was overdubbed to avoid an "R" Rating. MPAA policy stated that "fuck" could not be used to refer to intercourse in a PG-13 film.
Aaron Taylor-Johnson, who plays the teenage Eduard in the beginning of the film, also learned how to do the ball trick.
Jessica Biel replaced Liv Tyler, who dropped out of the film just as filming was about to begin.
According to the director's commentary, Jessica Biel dressed in a period costume for her audition.
The Illusionist is one of three 2006 films to feature both the topic of magic and magicians as main characters. The other two are Scoop (2006) and The Prestige (2006).
The character of Sofie was not in the original short story. Neither was the Crown Prince.
According to an article on production costs in Eastern Europe published by Bloomberg (August 25, 2005), the average extra on this film was paid around $30 a day.
When Eisenheim is performing at the Hofburg, he places the Crown Prince's sword upright on the stage. The first officer who attempts to lift it is unable. The second person to try, to whom the Crown Prince says "Not so eager, cousin", is also unable. That second person was probably meant to be Karl von Habsburg-Lothringen, who succeeded "Crown Prince Leopold's" father, Franz Josef, as Emperor in 1916.
When the Crown Prince was asking the Inspector if he saw Sophie and Eisenheim fornicating, the Prince's lips are clearly saying f***ing. The word fornicating was dubbed over so the movie could receive a PG-13 rating. Actors can use the f-word in a PG-13 movie if they are saying, for example, "I bumped my f***ing head!", but if the f-word is used in reference to sex, the movie will get an R rating.
The character Prince Leopold says during a performance of Eisenheim at the palace: "He tries to trick you ... I try to enlighten you. Which is the more noble pursuit?" This reference is to a famous slogan the RJ Reynolds tobacco company used in the 1930's that said "It's fun to be fooled ... it's more fun to know." The slogan was combined with adverts showing the secrets behind famous mysteries. The impetus for this was a tribute to the popularity of the American magician Horace Goldin.
The first time the Duchess appears on stage and begins to vanish their hands form into a clear homage to Michelangelo's fresco in the The Sistine Chapel.
Eisenheim's illusions are based on those of the great 19th century magician Robert-Houdin. Those prominently featured are "The Marvellous Orange Tree and "The Light and Heavy Chest".
The character portrayed by Philip McGough is shown in the credits to be named Dr. Hofzinser, after a prominent sleight-of-hand artist.