Factual error: When Red is sitting under the oak tree in 1967 and pulls the money out of the envelope, the top bill is signed by Nicholas F. Brady, who was Secretary of the Treasury September 1988 - January 1993. It's less about reading the handwriting as noting the different appearance of different signatures from different eras.
Factual error: Towards the end of the movie when Andy is escaping, he breaks open a sewage pipe and is covered with its contents. It is physically impossible for the sewage to shoot out of the break like it did. In order for that to happen there has to be pressure. But there is none there, because the end he crawls through is empty and the end is in the open air.
Continuity mistake: When Andy is playing the opera music, the whole prison stops what they're doing and stares at the speakers. When they show the infirmary, an African American man gets out of bed and looks out of the window. When the camera goes to the prison yard it pans around and goes right across the same African American man, who is now standing in the yard.
Continuity mistake: Andy is discovered missing. While the warden is walking to Andy's cell, he tells the guard to question "him", meaning the Morgan Freeman character. He points to Freeman with his left hand but when the scene changes its point of view he is pointing with his right hand.
Factual error: In the library, Heywood is listening to Hank Williams' "Lovesick Blues." He is playing the double LP "Hank Williams 24 Greatest Hits," which was originally released by MGM in 1970. "Lovesick Blues" was recorded long before this, but it is not possible for him to have acquired that particular 1970 double LP.
Continuity mistake: As Norton kills himself, the glass that blows out behind him is quite large and about half of the frame gets blown out. There are a few specs of blood on the window as well. A couple of shots later as the camera pulls back and shows Norton you can see the hole in the window is quite small and shaped differently and a smear of blood above the hole now.
Continuity mistake: When Norton prepares for his suicide you see on the desk a photograph and, a bit away, a lamp. After he has shot himself the photograph is leaning against the lamp (it was too far away in the previous shot to have fallen against it). There's some sort of card open on his desk on some paperwork which suddenly moves onto bare desk as well.
Continuity mistake: When showing how Andy switches the books, watch the folder on the table. The folder has a corner that is bent up. When Andy removes the Bible and folder from behind his back and places then on the table, the folder he places has the bent corner. The one already on the table is perfectly flat.
Continuity mistake: In the scene where Brooks Hatlen is committing suicide you see him engraving "Brooks was here" into the wood panel near the ceiling. The table he is standing on puts his face opposite the vertical wooden bars underneath the engraving (we see this in a shot looking up at him through these bars). Then when he rocks to tip the table over to hang himself he doesn't seem to fall at all, maybe a few inches if anything, yet when we see the pan out he has fallen at least 2 feet.
Visible crew/equipment: When Sgt. Hadley nearly throws Andy off the plate factory roof, the reflection of a boom mike is briefly visible in the shiny brim of Hadley's hat. Andy dropped the tar mop before approaching Hadley, and there are no other objects in this shot that could have caused the reflection.
Continuity mistake: When one of the "sisters" gets beaten up by Capt. Hadley he tries to escape from his cell and holds on to the bars on the other side of the passage. From the side his right hand grabs a diagonal bar, but seen through the bars he is holding on to a vertical bar.
Continuity mistake: When the warden is given a bribe by his contractor/buddy, it comes in a box containing a pie and the pie is in a disposable corrugated aluminium pie tin. The warden gives the pie to Andy in a later scene and when Andy and Red eat it, it is in a metal pie pan... the non-disposable kind.
Continuity mistake: During the scene where Andy and Red meet for the first time (baseball scene) the sun is in Red's face and so, Andy shouldn't have the sun in his face. But in fact, sometimes Andy has the sun in his face and Red doesn't anymore. Either they move very quickly between scenes or (probably) the whole scene were filmed at least two times.
Continuity mistake: In the same scene where Brooks is hanging himself, he carves his name and he is almost eye level with the spot where he is carving his name. The place where the rope is tied is lower. How come when he finishes carving his name he stretches to put the rope on? It is lower than where he was carving his name.
Continuity mistake: In the two different shots we have of Tim Robbins getting ready to put the book and folder into the safe for the last time (before he escapes) he collects the book and folder in two very different ways. First time he pulls the book towards the folder. Second time he brings the folder to the book.