During the final act (1832), Javert wears the medal of a Chevalier of the Legion of Honor. The medal is the modern version, a five-pointed Maltese Cross mounted on a green palm wreath. The period version had a bronze wreath.
When Javert gets the letter from Paris informing him that "Valjean" has been caught, the tricolor French republican flag is seen hanging in the street. But this scene takes place in 1823, during the Bourbon restoration. During this time (1815-30) the tricolor was not in use
The calf seen wandering in the barricades scene is a whitefaced hereford poll. That breed did not exist before the 1880, and did not reach France until the 20th Century.
The bishop is wearing incorrect liturgical vestments. He is shown wearing a dalmatic which is the vestment for a deacon with a stole worn 'priest-wise' on top. A french bishop of this period would have worn a 'fiddle-back' Latin chasuble with crossed stole underneath.
When a young child hops on the back of a horse drawn wagon, very clear views are given of the caliper disc brakes on the rear axle of the wagon. Brakes like this were not used until 1890 at the earliest.
When Thénardier is singing "Master of The House" and changing his hat/removing his glasses, he is visibly not moving his lips even though the song is playing.
During Jean Valjean's death scene after Anne Hathaway sang her first lines, she was seen ducking as she makes her way to her next position. This was visible when the camera was focused on Amanda Seyfried and Eddie Redmayne.
Sacha Baron Cohen speaks in different accents throughout the film; sometimes he has a British accent while other times he uses a comically bad French accent.
In "At the End of the Day" when all the women quickly form two rows the positioning of Fantine and the factory women standing on either side of her changes about three times.
When Gavroche first comes up from inside the elephant, he is wearing only a blue jacket. In the next shot, He is wearing a brown blanket. In the shot after that, it has disappeared again.
When Valjean gets down on one knee to tell Cosette of her mother's fate, he appears to reach up and take his hat off. When the camera goes from Cosette back to Jean, his hat is still sitting on top of his head.
When we first see Enjolras speaking before the crowd during "Look Down", he and Marius are holding pamphlets in their hands. When Enjolras sings his line "Where is the king who runs this show?", he raises his hand above his head and the camera does a quick cut for a close up -- revealing that the pamphlet has vanished from his hands.
When Javert arrives back at the barricade, the gun disappears and reappears in his hand.
During the final scene, the sky changes between shots from being cloudy to having few or no clouds.
When Thénardier and Madam Thénardier are being carried downstairs and out of Marius and Cosette's house, you can see Marius' ring both appear and disappear from Thénardier's finger.
During "The Robbery", Thernardier speaks to Javert and grows nearer and nearer to his face. The shot changes, however, and shows Javert at a different angle, moving closer to Thernardier.
During the opening scene at the docks, the sun keeps changing between shots.
At the beginning of "ABC Cafe," when Enjolras sings the line, "We need a sign," the part in his hair is suddenly on the other side.
In the "Master of the House" scene where Thénardier is fleecing his guests, there are signs for "glasses" and "eyes", and a menu that are all written in English, but should be in French.
Very near the end of the song "Stars," a shot from behind Javert shows he is facing Notre Dame and the moon is in the sky to his right. Although the moon is to his right and illuminates buildings in the background from that perspective, the light reflected off of Javert's forehead is coming from his left.
When Anne Hathaway sings 'I dreamed a dream', not all of her teeth are discoloured. Her own white teeth are visible (from her canines backwards) towards the end of the song.