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: 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)
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).