Shot entirely on green screen. Some exact shots from the original The Cabinet of Dr. Caligari (1920) were superimposed to properly replicate the original.
In the original 1920 film, Francis had no surname. In the remake, it is said by the Police Commissioner to be 'Geist' - this translates as 'spirit' in German.
In the original, there is no indication that Alan has any mental health problems. However, David Lee Fischer added the backstory to his reinvention of Alan that he was suffering from some kind of issue, for which he took medication. This gives a more rounded explanation of why he asks Cesare how long he has to live.