Deliberate mistake: When Sam and Frodo are in the field with the scarecrow, you can plainly see a car cruising past in the distance, from right to left. Further comment - there are two different shots which show the car moving from right to left. One starts at the top right distance, and in a shot a few seconds later the car has traveled down the road a bit and is more easily visible. Complicating matters is that the dust thrown up by the car looks similar to smoke from a chimney in the right distance, making some people think it is just the chimney. But chimneys don't move, and the smoke from the chimney is separate from the moving vehicle. [It is deleted on the DVD, but you can still see an obvious bit of image fakery on the hill just left of the smoking chimney. One can see the hill, tree, and surrounding area move up and down and shimmer slightly where someone has done a cut and paste to cover up the auto. The "car inclusive" scene appears on the National Geographic documentary, "Beyond the Movie The Lord of the Rings: The Fellowship of the Ring." Also, watch the music documentary on the Extended DVD - when it shows this scene the car is still in it. Bizarrely, in his commentary Peter Jackson said he never saw a car and doesn't know what people are talking about, but the production/post-production team say in their commentary that despite not thinking anyone would be able to see it, they took it out anyway.]
Deliberate mistake: At the beginning of the Fellowship's journey, they are resting on a hilltop (Hollin) with rocky formations. Bill the pony is tethered in the background in one shot. Then come the spying crows from Saruman and they all quickly hide. When the crows swoop in closer we see no-one, but who hid the pony and where?
Deliberate mistake: In the Chamber of Mazarbul, when Legolas lets loose the double arrows at the Troll near Balin's Tomb, in that shot he stands in front of the same wall as in the next shot. In this second shot he spins around, slices two Orcs and then looks at the Troll in front of him, only this second shot is flipped. In those two shots he stands in front of a solid rock wall with particular markings between two pillars. In the next shot it shows Legolas' back and the Troll down below as Legolas ducks down avoiding the Troll's chain flying overhead. Then in the next consecutive shot from the front again Legolas rises and is now standing in front of a stone wall that has a large alcove with books also between two pillars. These shots were spliced from a longer sequence because the two walls noted are adjacent to each other - in the film the alcove wall is to the left of the solid wall and they share a pillar between them.
Deliberate mistake: When Gandalf first sends the Hobbits on their journey, they are in the forest and the Hobbits walk up to Gandalf and the horse, you can tell that the Hobbits are dressed up little people rather than the actors themselves. You can tell by their stature, and how they walk.