Continuity mistake: When Inspector Uhl is inspecting the theater prior to the arrival on the prince, he is speaking with Eisenheim. When Uhl says "I have been puzzling over how it works", Eisenheim is standing with his arms behind his back. When it cuts his arms are crossed. (00:20:15)
Continuity mistake: Eisenheim holds Leopold's sword with a handkerchief underneath. Depending on the angle the handkerchief is messed up or folded neatly. (00:38:30)
Continuity mistake: When Eisenheim places the sword upright parallel to the floor, although it's supposed to be still, watch its blade and the design of the wooden floor and you'll notice its position keeps changing depending on the shot focusing it. (00:39:00)
Continuity mistake: When Leopold is trying to grab the floating sword, the position of his fingers on it differs depending on the angle focusing. (00:40:15)
Continuity mistake: Eisenheim ends his show to Leopold and the Duchess turns her head away in slo-mo. When the angle changes half a second later she is staring at him and repeating the previous movement. (00:41:45)
Continuity mistake: The Duchess arrives at Eisenheim's house horseback riding, her hair loose and messed up. She talks to him, kisses him, and a second later, when she enters the house her hair is perfectly brushed. (00:43:00)
Continuity mistake: At the start, in shots from the stage towards the audience, all of the fires are lit, but in a closer shot of the audience near the front of the stage, at least one of the fires is out. During the final illusion shown at the end, the same shot or at least very similar to the one used at the beginning shows the same mistake again. (01:28:25)
Continuity mistake: After Eisenheim has disappeared, literally, from stage, Uhl and the policemen search his office. There, Uhl finds Eisenheim's notebook with the design of the locket in it. There is a large tear in the middle of the paper. It disappears when the inspector looks at it again after he has found the locket in the Prince's barn. (01:31:00 - 01:31:45)
Continuity mistake: After Eisenheim's disappearance, when Inspector Uhl finds the paper with the detailed diagrams of Sophie's locket, all of the writing and drawings are completely different in the close-up of the diagrams, later at the stable.
Answer: Although the story is fictional, some of the details are based on the life of Austrian Crown Prince Rudolf, only son of Emperor Franz Josef. The painting of the emperor which Eisenheim creates is an actual portrait of Franz Josef. (from IMDb).