Paul Henreid was loaned to Warners for the role of Victor Lazlo by Selznick International Pictures against his will. He was concerned that playing a secondary character would ruin his career as a romantic lead.
Conrad Veidt, who played Maj. Strasser, was well known in the theatrical community in Germany for his hatred of the Nazis, and in fact was forced to hurriedly escape the country when he found out that the SS had sent a death squad after him because of his anti-Nazi activities.
Conrad Veidt's wife was Jewish and that is one of the reasons why Veidt had to flee Germany before his wife or himself was arrested.
Michèle Morgan asked for $55,000, but Hal B. Wallis refused to pay it when he could get Ingrid Bergman for $25,000.
Howard Koch was instructed to start the screenplay all over again, paying particular attention to Rick's background and the ending, while the Epsteins were struggling with their version. Writers Casey Robinson and Lenore J. Coffee were asked to critique the two versions and found much merit in both, though Robinson thought the romantic angle lacking and was subsequently tasked with ramping this up.
Joan Alison always envisioned Clark Gable as Rick, who "was my concept of a guy that I would like... I hated Humphrey Bogart. I thought he was a common drunk."
A $100,000 insurance policy was taken out on the films leading player, Humphrey Bogart, in case he died during the film's production.
After hearing the French message via the loudspeaker Rick predicts "Nothing can stop them now. Wednesday, Thursday at the latest they would be in Paris". In fact, the Germans entered Paris at the morning of June 14th, 1940 - Friday.
After shooting, Max Steiner spoke against using "As Time Goes By" as the song identifying Rick and Ilsa, saying he would rather compose an original song in order to qualify for royalties. However, Hal B. Wallis replied that since the filming had ended, Ingrid Bergman had cut her hair very short for For Whom the Bell Tolls which was shooting at a distant locale and she therefore could not re-shoot already-completed scenes that had used "As Time Goes By".
Although M.K. Jerome and Jack Scholl are listed in the opening credits for "Songs", they are in fact represented by only one song (Knock on Wood). The other song they wrote for Casablanca (Dat's What Noah Done) was cut from the picture.
Although this was an overtly anti-Nazi film, it wasn't the first one that Warner Bros. had made (it had come out several years earlier with Confessions of a Nazi Spy). Warners was the first Hollywood studio to be so open about its opposition to the Nazi regime, and the first to prohibit its films from being distributed in Nazi-occupied territories. Indeed, Harry M. Warner was making speeches denouncing Nazi activities in Germany as early as 1936.
Around nine minutes into the movie, Rick OKs a credit slip dated 2-Dec-1941.
At a salary of $25,000 for five weeks' work, Conrad Veidt was the highest-paid actor on the set and on loan from MGM. His main competition for the Maj. Strasser role was Otto Preminger, under contract to 20th Century-Fox, for whom Darryl F. Zanuck had demanded the outrageous sum of $7,000 per week.
At one point it looked like there was going to be trouble casting a foreign actor in the part of Victor Laszlo. Herbert Marshall, Dean Jagger and Joseph Cotten were considered until Paul Henreid became available.
Because the film was made during WWII they were not allowed to film at an airport after dark for security reasons. Instead they used a sound stage with a small cardboard cutout airplane and forced perspective. To give the illusion that the plane was full-sized, they used little people to portray the crew preparing the plane for take-off. Years later the same technique was used in the film Alien, with director Ridley Scott's son and some of his friends in scaled down spacesuits.
Captain Renault's line, "You like war. I like women," was changed from "You enjoy war. I enjoy women," in order to meet decency standards.
Carl's back story is hinted at once, when he is referred to as "Professor" by a waiter.
Casablanca, Morocco, was one of the key stops for refugees fleeing Nazi-occupied Europe, which is why the original playwrights chose the city for the setting of their play (though initially they had opted for Lisbon).
Director Michael Curtiz' Hungarian accent often caused confusion on the set. He asked a prop man for a "poodle" to appear in one scene. The prop man searched high and low for a poodle while the entire crew waited. He found one and presented it to Curtiz, who screamed "A poodle! A poodle of water!" See also The Charge of the Light Brigade.
Early in the production, studio head Jack L. Warner offered the role of Rick Blaine to George Raft, but the actor turned it down. As the shooting script took shape, producer Hal B. Wallis began to envision actor Humphrey Bogart in the Rick Blaine role. As Bogart was under contract to Warner Bros. the role was assigned to him by Wallis. But after Bogart had been cast in the role, George Raft reconsidered his decision and contacted Warner to deliver the news that he had decided to accept the 'Casablanca' part after all. After consulting with Wallis - who had never envisioned anyone but Bogart in the role - Warner decided to support his producer: Warner explained to Raft that Humphrey Bogart had been cast in the role of Rick Blaine, and that the part was no longer available.