The letters of transit that play such a key role in plot points throughout the film did not actually exist in Vichy-controlled France - they were invented by the writers. Joan Alison would always say she’d expected somebody to pick her up on it, but nobody ever did. 29/53

In pre-production, writer Casey Robinson had been hired for edits, including some of the romantic scenes between Rick and Ilsa. He was offered credit but said because at the time he was only taking credit for scripts he wrote himself. He did himself out of an Oscar. 30/53

Mentioned above, Broadway producers passed on the script as, originally, Ilsa was not a ‘virtuous’ woman. She was living with a married man and when she and Victor came to Casablanca, they weren’t married. This had to change as film censorship of the time didn’t allow it. 31/53

Similarly, Captain Renault's line "You like war. I like women" was changed from "You enjoy war. I enjoy women.” This was at the demand of censors from the Production Code's Office. 32/53

Due to wartime restriction, the majority of sets were recycled from old Warner Bros productions. One of the few original sets was Rick’s Cafe. It was based on the Cinema Vox in Tangier, Morocco, the biggest theatre in Africa at the time. 33/53

As Time Goes By was written by Herman Hupfeld for the Broadway musical, Everybody's Welcome. Hupfield had been a college roommate of Murray Burnett and the song was written into the play. After the film was released, the song stayed on the US Hit Parade for 21 weeks. 35/53

Max Steiner tried to have As Time Goes By removed from the film as it wasn't his. He said he’d rather write something original (and receive royalties). However, since filming, Bergman had cut her hair short for For Whom the Bell Tolls so reshoots weren’t possible. 36/53

Two other composers - M.K. Jerome and Jack Scholl - are credited in the titles for "Songs." They actually have just the one son in the film, called Knock On Wood. ("Knock on Wood"). The other song they wrote, Dat's What Noah Done, was cut late in the edit. 37/53

The opening scene is the famous map sequence with narration that explains how WWII refugees ended up in Casablanca. The sequence was actually created by a young Don Siegel, who would go on to direct Invasion Of The Body Snatchers and Dirty Harry. 38/53

The first time we see Rick is a shot of him playing chess - Bogart’s own favourite pastime. The position of the pieces was from a game of Bogart's that he was playing via mail correspondence. 39/53

The first scene is one of the Paris flashbacks. Bogart apparently said "I'm not up on this love stuff and don't know what to do". The script wasn’t finished, so Bergman didn't know whether Ilsa was meant to be in love with Rick or Victor. Curtiz said “play it in between." 40/53

Dooley Wilson was a professional drummer, not pianist, so had to fake his playing as Sam. The music was recorded live on the set by session musician Jean Vincent Plummer, who was sat behind a curtain so Dooley could watch and copy his hand movements. 41/53

Curtiz himself was a Jewish-Hungarian immigrant, and his accent caused some confusion on set. One time, he reportedly asked a prop man for a "poodle". When the prop man found one and brought it to set, Curtiz yelled: "A poodle! A poodle of water!" 42/53

Filming the famous scene in which La Marseillaise is sung to drown out Die Wacht am Rhein, many extras were real refugees and cried on the set. The scene was inspired by La Grande Illusion from 1937, where French soldiers in a POW camp sing the song as an act of defiance. 43/53

The Rick’s Cafe singer seen sitting on a guitar in the La Marseillaise is Corinna Mura. She was a cabaret actress and singer, and stepmother of Tony Award-winning artist Edward Gorey. 44/53

Because filming took place after Pearl Harbour, airports couldn’t be lit after dark for fear of making it a bombing target, so the famous finale was shot on a sound stage with a cardboard airplane. To give the illusion the plane was huge, little people played the crew. 45/53

There were plans for a final scene. We saw Rick, Renault and a group of French soldiers on a ship. The idea was to incorporate the Allies' real 1942 invasion of North Africa. It was scrapped when Wallis said "it would be a terrible mistake to change the ending." 46/53

The famous poster features an illustration of Bogart as Rick wielding a gun and wearing a fedora. It was copied almost exactly from a shot from the Bogart-starring Across The Pacific. Artist Bill Gold repainted it to be photorealistic. 47/53

Due to its anti-Nazi theme, the film was not released in Germany until 1952. Even then, it was shown heavily censored with all references to Nazism removed. Resistance fighter Laszlo became a Norwegian atomic physicist and the La Marseillaise sequence was deleted. 48/53

At the Oscars, Casablanca won Best Director for Michael Curtiz. And when it won Best Picture, WB head Jack Warner went up before producer Hal Willis, who was enraged, and left WB shortly after. Academy rules were later changed so producers, not studio heads, get the award. 49/53

The film also won Best Screenplay, making Julius and Philip Epstein the first Oscar-winning twins in history. 50/53

On a budget of approximately $900k, it took $6.9m at the box office, making it a huge hit. And today, Casablanca is widely regarded as one of the greatest and most influential films to come out of Hollywood. 51/53

Because of the success of the film, Warners had plans for a sequel, to be called Brazzaville. Bergman wasn’t available, so Geraldine Fitzgerald was lined up to play Ilsa. It was rumoured to follow Rick on the trail of Nazi agents in Tangier, but the idea was scrapped. 52/53

Finally… things could have been oh so different. Casablanca was chosen as the setting for the play (then film) as it was one of the major stops for refugees fleeing Nazi-occupied Europe. Originally, though, it was going to be set in Lisbon. 53/53