Revealing mistake: The scene of rioting in the UK features a load of police officers running through a crowd. All the officers shown are wearing black tunics and custodian helmets worn with chinstraps. This is obviously old stock footage from a protest in the 80's or early 90's as nowadays, (and especially in 2012) the tunic has not been worn as general wear for well over 15 years, and Brit cops are now better equipped for protests with body armour, NATO helmets, flame retardant overalls, etc.
Revealing mistake: When Barnes and Marcus Wright are helping John Connor back to the chopper and when Barnes gets in the helicopter, he's revealed to be a stand in. It's in plain sight, at the right side of the screen. (01:41:20)
Revealing mistake: At the Smithsonian Air and Space Museum, there is a triangular enclosure around Jetfire that amusingly just fades away and vanishes as Jetfire transforms. (01:23:05)
Revealing mistake: When the old couple who give Wolverine clothes are first driving towards their house, there is an aerial shot of them driving over a bridge. This is supposed to be set in Canada (drive on the right) but it was filmed in New Zealand (drive on the left). They are driving on the right but the arrow on the road is on the left side.
Revealing mistake: Throughout the movie closeups of Enik's eyes reflect the lights and set around him that aren't part of the movie. During the scene when he's talking to Dr. Marshall about how the crystal controls the sleestack, you can see the white ceiling of the soundstage and lights which instead should be the sky.
Revealing mistake: During the final confrontation in Veidt's lair, you see the actor Billy Crudup in his SFX suit reflected in Nite Owl's goggles, not the image of Dr. Manhattan.
Revealing mistake: Susan appears to pass right through the glass window after knocking down Gallaxhar.
Revealing mistake: During the four-year flashback scene in East Africa, after the building is bombed, two helicopters fly to the right of the building. However, because they are CGI, the telltale whirl (or any movement) the blades should have made in the smoke isn't there. (00:50:10)
Revealing mistake: Just after the submarine crew see all the whales passing them by, the shot switches back to the helicopter and all the dials on the console. If you look closely, you can see that the image has been flipped as all the words and numbers are the wrong way around. (00:05:20)
Revealing mistake: When the Federation fleet is preparing to warp to Vulcan, you'll see the first ship blast off, but the second ship blasts off out of nowhere. You could argue that the ship was out of sight and below the Enterprise, but the light trail isn't that long. The light trail starts in front of the Enterprise where you should be able to see a star-ship. (00:40:45)
Revealing mistake: When Needy uses her key to unlock the door, you can see the door is already open. (00:58:07)
Revealing mistake: In the scenes where Sam 1 and Sam 2 are in touch, the double is completely wrong. Wrong hair, wrong profile and wrong hind end.
Revealing mistake: The movie shows in Matrix-esque slo-mo the double baton swing Goku dodges, from Fuller and his goon. They are nowhere near hitting each other, and yet, this missed baseball-bat swing causes them to KO each other in close-up. (00:16:55)
Revealing mistake: When the Sheriff is in pursuit of the black SUV, there is a particular shot of the Sheriff's car doing a wide right turn and you can see that it's a young bald stunt driver, completely unlike the older, full head of hair Bruce Boxleitner.
Revealing mistake: When Steven Seagal makes his triumphant entrance in the credits, his sword misses the first zombie he supposedly hacks (right after "Written by"), by a mile. (00:03:20)
Revealing mistake: When they drive out of Vegas, headed for Witch Mountain, there is a shot that appears to be made with a camera on a mobile cherry picker. The camera sweeps across the road and up high, watching as the vehicle passes under the camera. As it passes the camera, you can see a trail of dust that was kicked up by the cherry picker. It crosses the road and is still floating in the air from a recent crossing.
Revealing mistake: When the soldier is tempering, you can see sparks fly before the hammer hits the metal.
Revealing mistake: Nick's reflection is seen in the shiny ceiling, but the guns floating above him have none, revealing this to be a CG effect. (00:54:50)