When Orcs attack the fellowship in the Chamber of Mazarbul (the crypt in Moria), Frodo's sword glows blue, but Gandalf's does not. Gandalf carries Glamdring, the Foe-Hammer, which was forged by Turgon the elf and therefore should glow as Sting does.
When Gandalf is on his cart walking up to Bagend with Frodo the camera zooms out and pans around the Shire, ending up looking over some of the homes. If you keep looking at the sky you can see a blinking plane light just before it goes back to a close up of Frodo and Gandalf.
Many viewers spotted a car in the background of the theatrical version when Sam says that he is now the furthest he has ever been from home. In a 1 December 2003 Newsweek article, director Peter Jackson confirmed this, and revealed the car had been removed digitally for the DVD release. Jackson says: "We actually didn't know about the car until we were cutting the movie. The smoke and dust wasn't so bad because there was already lots of it around, but the bloody windshield was reflecting the sun back into the camera lens. So we erased it for the DVD. I think some people were upset because they tried to show it to their friends and it was gone." (The infamous car can be seen on the "Academy DVD" which was created for the Oscar jurors and leaked on the Internet. Also, the unaltered shot with the car appearing in it is contained in the bonus material of the SEE DVD - the feature about the film score.)
In Hobbiton, Gandalf's cart pulls away from the Hobbit children who are begging for fireworks. When the camera angle is looking back at the children from the viewpoint of the cart, there are treaded tire tracks in the dirt of the road.
Gandalf asks Frodo if he can see anything on The Ring after he removes it from the fire. Frodo says "Nothing. There's nothing". The camera switches over to Gandalf then Frodo says "Wait!" The camera goes back to The Ring in Frodo's hands. It is plain in appearance and then letters start to appear on it. Why did Frodo say "wait" if nothing had happened yet?
When Sam reveals to Gandalf what he overheard of Gandalf's and Frodo's conversation, a map disappears and reappears under his right shoulder. The fallen books on the floor also change position between shots.
In the duel between Aragorn and Lurtz, Aragorn is thrown against a tree and we see his sword fall from his hand. The next shot shows Lurtz throwing his shield pinning Aragorn to the tree and again we see his sword fall from his hand.
While the four hobbits (Frodo, Sam, Merry, and Pippin) are at The Prancing Pony in Bree, Merry returns from the bar with a pint and Pippin takes off to get his own. When the angle changes to an over-head shot, Merry is no longer at the table and Pippin is suddenly back in place. This was obviously a shot that carried over from the previous scene (prior to Merry's return from the bar).
When Gandalf first appears riding on his cart, there is a long grey-green cloth hanging from the lantern on the right-hand side of the cart, with Gandalf's staff on the left. In the next shot, the lantern and cloth have switched sides with the staff (which itself moves back and forth between shots as Gandalf and Frodo travel into the village). It would seem that the first shot has been flipped so that the "road" bends round to the left to match the curve of the road as Gandalf approaches Frodo in the next shot.
When Gandalf arrives at the hobbit village, he lauches some fireworks and the children cheer and jump with their hands in the air. In next shot, at least one of them (to the right of the screen) has both arms pressed to her body.
Immediately after the Riders are overtaken by the river, a shot of Arwen shows her right arm (holding the sword) lowered. In the next shot, her arm is raised high over her head, as though she were still challenging the riders.
When Saruman first attacks Gandalf he uses his staff in his right hand. In the next shot from behind Saruman he is holding his staff with his left hand above his right hand, but in the next shot from the front it is back with his right hand above his left.
During the fight between Gandalf and Saruman, Saruman closes all the doors in the tower. During the fight Gandalf is thrown around a lot and you can see one of the doors open, but in the next shot Saruman is thrown at this door which then breaks open (again).
In the palantir scene between Gandalf and Saruman, Saruman says that the eye of Sauron sees past all, including flesh. In that shot a ring can be seen on Gandalf's finger (one of the three elvish rings). Then Saruman says, "You know of what I speak Gandalf," and in the very next shot, the ring is gone.
When Frodo leaves the fellowship to continue on his own to Mordor, there's a tear running down his right cheek. When we next see him, the tear is on his left cheek and there is no evidence of it being on the right side. In the extended DVD version, there are tear tracks on both sides of Frodo's face.
When Arwen is riding her horse to get Frodo to Rivendell, Frodo is seen with green pus on his face by his mouth and eyes. In the next clip of Frodo, the pus is gone with no signs of it being there before.
When Frodo runs up to the edge of the grassy knoll to tell Gandalf he's late, it's obvious he's a good few feet away from the wagon once it's stopped. After Gandalf is done talking and it goes to the shot where Frodo leaps into his arms, the wagon is standing right next to the grassy knoll, much closer than it was in the previous shot.
In the scene at Isengard in which Orcs are tearing down trees, we see it start to rain as the camera focuses on Gandalf on the top of the tower, but in the scenes with Orcs and Saruman, the weather alternates between rain and no rain.
When the squid-like Watcher of Moria catches Frodo by the ankle and pulls him back Frodo should have fallen on his face and been dragged back on his front. Instead, he falls backwards and is on his back when being pulled into the lake.
As Frodo catches a ride on Gandalf's cart through the Shire, in close-ups, sunlight is brightly shining on Frodo's face from the right, but in close-ups of Gandalf sitting beside him, the sunlight is coming from above and left.
When Bilbo opens the door of his house to greet Gandalf, the wizard raises his hand from his side when he says, "Bilbo Baggins!" However, in the next shot, his hand is back at his side as if he hadn't moved.
In the Extended Edition, when Gandalf begins to speak in the language of Mordor, a long shot of Elrond is seen, at which point he puts his hand on his forehead. In the close-up immediately afterwards, his hand is down and he again puts it to his head.
When Gandalf and Frodo are discussing the ring at the table in Bag End, Frodo is holding the kettle and pouring water while Gandalf is speaking. When Gandalf finishes his sentence the camera angle changes to a closeup of Frodo who is holding a cup with both hands.
When Frodo crouches back from the Ringwraiths on Weathertop, the Ringwraith closest to him has a sword in his right and a knife in his left hand. After Frodo puts on the Ring, the Ringwraith's left Hand can be seen - but the knife is gone.
After Gandalf pounds his magical staff into the stone on the bridge of Khaza-Dûm, a wideshot is shown in which the head of the staff is on the left side of his face (our left), but in the following close-up, it is on his right
After Bilbo's birthday party, Bilbo enters his house and takes off the ring. He then steps over to a walking stick, picks it up with his left hand and transfers it to his right hand. In the very next shot the stick is back in left hand, and what appear to be a couple of small maps are now in his right hand.
When the first Uruk is "born" and he kills the Orc standing next to him, he is muddy and his arms are not on his chest. In the next shot of him standing up, the mud is gone and replaced with slime and his arms are crossed on his chest.
After getting off the boats, there is a scene with Gimli talking with Aragorn. Inbetween shots, behind Gimli, Sam switches from sleeping to awake, then back to sleeping. Later, he opens his eyes when Frodo is revealed to be missing.
When Frodo falls down in the snow and Boromir hands him the ring, Aragorn's right hand has clearly been removed from the sword hilt. However they immediately show a close up where his hand releases the hilt.
When the fellowship is departing from Lothlorien, Galadriel is seen riding in the swan boat across the river. If you look into the background to the left of the screen, a crew member can be seen crouching down and looking about.
At the council of Lord Elrond, once the fellowship has been formed, in the close-ups of the hobbits you can see that they measure up above Gandalf's beard and Legolas's hair, almost up to their necks, but in the wide shots of the whole fellowship they are clearly smaller - only about waist height.
When Aragorn and Legolas are talking, after the Fellowship has stopped before the Falls of Rauros on the River Anduin, the river can be seen flowing from right to left in the back ground. They are on the West bank of a river flowing from North to South and dropping over a large waterfall: the water should flow from left to right.
When the company are traveling South in the boats on the River Anduin, Legolas becomes aware of the approaching Uruk Hai. He turns his head to the left. The chief Uruk, Lurtz, turns his own head to the right. This implies that the Uruks are on the East bank of the river but in fact they are on the West bank, having come on foot from Isengard. And in crossing the river to get to the Emyn Muil Frodo goes beyond the Uruk's reach.
The same ring that is the right size on the enormous Sauron also fits snugly on the tiny Frodo. The book explains that the ring can conform to fit its current master, and the movie shows it subtly shrinking or expanding.
Gandalf loses his staff when he is imprisoned by Saruman, but later he has it again. Or so it seems. Actually, it's a visibly different staff. He also seems to lose his hat, but he leaves it on his horse, whose fate is never established. Bill the pony remembers his way back to Bree in the book after he is released by Sam at the entrance to the mines of Moria. In the book, Gandalf stops at Bree just before being imprisoned and shortly after escaping. It doesn't seem implausible that his horse could have remembered its way back to Bree or maybe even Rivendell. Gandalf could have retrieved his hat when he made his way there himself.
The main Ringwraith on Weathertop draws its sword twice as it approaches Frodo. However, this stuttering image may be deliberate. Before Frodo puts on the Ring, we can see all of the Ringwraiths draw their swords. After Frodo puts on the Ring, the main Ringwraith draws a short sword. The long sword for a sword fight, keeping one's opponent at sword's length. The short sword for Frodo's execution, since he didn't put up a fight there was no need for the long sword.
When Frodo saves Sam from drowning, they clasp each other in the "acrobat-grip", they both clasp the other one's wrist, a very tight grip. However, when Sam's hand is pulled above water, his arm has turned 180 degrees. It is, however, possible for a drowning, thrashing man to loose his grip and get turned around, even when getting rescued.
When the Black Rider comes into shot while the hobbits are hiding under the tree-roots, he appears on the left-hand side of the tree without first being visible on the right-hand side. This is probably deliberate, to be a shock.
When Frodo is looking out at Rivendell from the balcony, we see his hands on the rail. The rail only comes up to his waist, and he can comfortably rest his hands on it. As Rivendell is an Elven city, the rail should be above his head. However, as Bilbo has been an honored guest in Rivendell for several months it is likely that these are Bilbo's rooms, and they have been modified for him (by the elves).
When Legolas spots the "crebain" birds from Dunland and warns the fellowship to take cover, his eyes are brown. Yet as an elf and the rest of the movie his eyes are blue. This is because Orlando Bloom had to wear contacts to change the color of his eyes, but could not wear them consistently because they scratched his corneas. Most of the time, his eye color was digitally changed, but they missed it in this shot.
After the Ring Wraiths break down the entrance to the village (the scene after Aragorn talks to Frodo and the others at the prancing pony), one ring-wraith turns toward a light and you can see the mask which hides their face but allows them to see out (like the Halloween masks). A ring-wraith is supposed to have no physical form other than when they are being looked at with the ring.
The forced perspective trick becomes visible while Gandalf and Bilbo are having tea. As Bilbo is pottering about, Gandalf sits on a Hobbit-sized chair at a table that is too small for him. As he shuffles slightly to get comfortable, his knees move the table, but only his, smaller, half moves - the other half, where Bilbo is seated, is further away from the camera, and stays put. It can be seen that this gap between the two table "halves" is concealed behind cleverly placed, bottles, plates, etc. Then, when Bilbo is about to pour hot water in the teapot, Gandalf lifts the teapot lid for him. The lid is not on the teapot, but placed on a spike nearer to the camera to create the forced perspective. It is also clearly visible when Gandalf puts the lid back.
In the theatrical version, Saruman's lower legs disappear for a frame or two as the camera swoops toward him when he is standing on the summit of Orthanc, bringing the lightning down on the mountain. This has been corrected in the extended edition of the film.
It is clear, that in some long shots of the scene in which the fellowship is formed in Rivendell, smaller stand ins (resembling children) are used to contrast height and are clearly not Elijah Wood, Sean Astin, Dominic Monaghan or Billy Boyd.
Aluminium foil can be seen inside the chimney passing under the camera as Gandalf rides into Hobbiton, just before the kids ask for fireworks. The foil is probably used for containing dry ice or such, to make a smoke effect in the chimney.
After the huge orc battle, one of the "dead" orcs sits up and has a good look round before lying back down. This has been explained away in all manner of different ways, but it strikes a sufficient number of viewers as incongruous that it seems more likely to be a genuine error than not.
When Boromir cuts his finger on the broken sword, the blood is visible on his finger behind the sword before he gets cut, and as the sword is pulled away, his undamaged fingertip is visible through the blood.
During filming Christopher Lee broke his finger. As Saruman is summoning the lightning when the fellowship are climbing Mount Caradhras, as the camera swoops past Saruman you can see Lee's heavily bandaged finger.
When Sam is nearly drowning in the river, you can see that the bubbles are placed later. There is no distortion of light from the waves, and his hair and cape are being moved as though by wind, showing that he was on strings above a fan on a green screen.
Aragorn finds "athelas" aka "kingsfoil" to tend Frodo's wraith-inflicted wound. He pulls a small knife to cut away what he needs, which on closer inspection can clearly be recognized as a common switchblade.
When Boromir is fighting the Uruk Hai the first arrow is shown as piercing his left shoulder. A second arrow is then shot at him and shown to strike in exactly the same position. The camera then shows a wider angle shot where he has one in his shoulder and one in his gut. This is on the Australian DVD version.
As Boromir lies dying, Aragorn leans over him. In the shots over Aragorn's shoulder, looking at Boromir, Boromir's right hand rests on Aragorn's left shoulder. In shots looking at Aragorn, the hand is not there. This is because these shots looking at Aragorn while he is speaking to Boromir were actually shot without Sean Bean.
When the Balrog snares Gandalf at the bridge of Khazad-Dum with its whip and pulls Gandalf to the edge of the broken bridge, the bridge surface is smooth and no ridges are visible all the way to the edge of the broken bridge. The tracks left by Gandalf's hands in the dirt on the bridge further indicate that. However, in the next shot when Gandalf is clinging to the bridge, just before he says, "Fly, you fools," there is a ridge that Gandalf uses to grab on that is not present in the previous shot.
When we enter the chamber of Balin's tomb, there is a shaft of daylight through the far wall. Soon afterward, we leave the chamber and a similar shaft illuminates the stone above the chamber door; this light must come from roughly the opposite direction.
At the end of the film, there is a wide shot showing Merry being carried off by the Uruk-hai. It is clear that the full-sized, 5-foot-7 Dominic Monaghan is in the shot rather than the scale double - his feet hang way down below the Uruk-hai's hips.
At the end of the movie, when Aragorn decides that he, Legolas and Gimli will go to save Merry and Pippin, Legolas's arrows are first yellow, then green, then yellow again. Even more strikingly, in this scene, "Gimli" clearly appears in a forbiddingly close mid-shot as Scale Double actor Brett Beattie, then shifts to the more correct John Rhys-Davies. At a head or more shorter than Aragorn and Legolas, Beattie could barely pass as size-appropriate to be filmed with Legolas and Aragorn in crowded scenes, wide shots, back-to-camera, etc., but his face should never have been so clearly exposed, so close to the other actors.
When Lurtz is about to finish off Boromir, and Aragorn comes out of the right side of the screen to attack him, you can easily see that "Aragorn" is a dummy on strings. As it flies in from the upper right, it hovers for a split second before crashing into Lurtz.