The Phil Caputo book, "Equation of Evil" seen in Hollis Mason's apartment next to the television during the Rorschach/Patterson-Gimlin Film news footage, was not published until 1996. Even in the alternate history, this book probably would not have just happened to exist 11 years early.
During the Kennedy assassination scene, the police are seen riding newer (Post 1994) Harley-Davidson FLH Police models. In 1963, Harley's FLH models only came with spoke wheels, one front brake disk, and the rear shocks were forward of saddlebags and visible, not hidden behind the saddlebags as shown.
Doctor Manhattan describes a "circulatory system" appearing on the grounds of a government base. However what is depicted is clearly the nervous system, as it features a brain and spinal cord, but no heart or lungs. (This error is repeated from the novel.)
When Adrian/Ozymandias is being interviewed in his office the reporter states that he is the second Watchmen to reveal his secret identity the first being Hollis Mason/Nite Owl I. Mason was a member of The Minute Men (the precursor to The Watchmen) which didn't form until he had retired and passed the Nite Owl mantle to Dan.
After the picture of all 8 of the the Minutemen are shown in 1940, Hollis Mason is speaking to Daniel Drieberg and starts to name all of the Minutemen and leaves out the Silhouette...Mason says "It was me, Dollar Bill, Mothman, Captain Metropolis, Hooded Justice, Silk Specter, and the Comedian. Oh don't let me get started on him".
(at around 29 mins) When Rorschach breaks into the Rockerfeller Military Complex and starts to name the Minutmen and what happened to them...Rorschach mentions the first Night Owl, the first Silk Specter, Dollar Bill, Silhouette, Mothman and Adrian Veidt (aka Ozymandias), but fails to mention updates on Captain Metropolis and Hooded Justice and what happened to them.
When Rorschach jumps out of the window of Moloch's house and is fighting the police, one of the officers is standing and watching on the doorstep, while all of his fellow officers are rushing to fight Rorschach.
When Nite Owl and Silk Spectre II first arrive at the prison riot, the first one to run at them is an inmate with long hair. Silk Spectre II kicks him to the ground. As they fight their way down towards the guard, the same man is seen again and he is then swept off his feet and clotheslined to the ground by Nite Owl.
In the main titles, Nite Owl stands up and his head completely covers the "1940" on the sign behind him.
In all subsequent shots of the photograph of "Minutemen 1940" the banner hangs unobstructed above his head.
When Rorshach kicks in the door at the child murderer's house, the door bounces several times against the wall, showing a spring is holding it open so it won't swing back in the actor's face. When the murderer gets home a few minutes later, it's standing only an inch or so open.
In Dan Dreiberg's underground laboratory, Rorschach rather pointedly drags his finger through a thick coat of dust over a cover on his work bench to indicate its lack of use. Later when Laurie Juspeczyk pulls the dust cover off of the "Archimedes" ship, there is no cloud of dust.
In the beginning of the movie when the Comedian (Edward Blake) is thrown through the glass window, midway down his body turns face down to the concrete (which matches how he dies in the comic book). Yet when the camera shows the Comedian he is lying on the concrete face up instead of face down.
When Rorschach searches the Comedian's apartment following the crime scene investigation, after jumping from the window he searches the place with his flashlight. He shines his torch to his left (towards to kitchen), but the next shot shows the light shining over the picture of Sally Jupiter with the knife stuck in it (the opposite side of where he points his flashlight).
(at around 5 mins) During the opening fight, as the Comedian is thrown across the room, Director Zack Snyder can be seen huddling between the drawer and brick wall, lower, left-hand corner of the screen. (Snyder points this out during his "live" Blu-Ray commentary.)
In the Mars scenes, two moons of approximately the same size as ours can be seen in the sky. However, the larger moon, Phobos, is 1/4 the apparent size of our moon when viewed from Mars, the other moon, Deimos, is much smaller - 5% of our moon's apparent size. Neither moon is as spherical as depicted, nor clearly visible from the surface.
During funeral of The Comedian, the Soldiers making up the funeral detail are all wearing black berets. The black beret was adopted by the Army Rangers in 1979 as their official head gear.The movie is set in an alternate version of 1985, and at that time soldiers that were not part of the Army Rangers would have been wearing the U.S. Army Garrison Cap (otherwise known as a Service Cap) which is green and roughly the size and shape of a business envelope. The Army made the switch of headgear under the direction of General Eric Shinseki. The beret is worn with a blue "flash" with his/her unit insignia centered on it, further identifying that the troops in the movie were not Army Rangers.
When Kennedy was shot the Zapruder film shows a traffic sign passing between the camera and Kennedy's car. This has been a fact of endless frustration for investigators since the first shot hits as the car is behind the sign. In the Watchmen scene of the shooting there is no sign near the spot of the shooting. The only sign I saw was at least a couple hundred yards down the street.
During the opening credits shortly after the plane dropped the atom bomb you can see the image of Miss Jupiter on the side of the plane waving a U.S. flag with fifty stars. Back then in 1945 the US had the 48 star flag, 6 rows of 8 stars.
When the coffin is being lowered into the grave Dr. Manhattan's glow is not reflected off of it. This is because Dr. Manhattan can turn off the glow if he so chooses. One would not be glowing at a funeral, so Dr. Manhattan in turn is not.
In this movie, the United States won the Vietnam War. However, one of Veidt's monitors is playing Rambo: First Blood Part II, a movie about avenging America's losses in Vietnam. In Veidt's world, Rambo must be regarded as an imaginative science fiction movie set in an alternate universe.
If you look closely at all the framed newspaper articles, especially in the opening credits, the articles themselves are just series of repeating texts and paragraphs. However, this may be intentional, as it is a convention in comic books/graphic novels for "minor text" to appear as scribbles or repeating text.
Dreiberg microwaves a carton of Chinese food with its metal handle still attached. While microwave instructions commonly prohibit customers from placing metal inside them for safety reasons the dangers of doing so are greatly exaggerated in the public mind. Small amounts of metal, like the handle from a Chinese food container, will likely not cause sparking and will generally, at most, cause damage to the microwave not a larger fire or an explosion.
Some of the floating credits are reflected in Neil Armstrong's helmet. The back of the letters (or the reverse side) is what is facing the helmet. The reflection of the reverse side (or, the reverse of the reverse side) would show the text properly oriented. Therefore, both the credits and the reflection should appear as readable; the reflection should not appear backwards.
When the reporters are talking to Veidt in his office, they refer to him as being only the second hero to reveal his identity, after Hollis Mason. It is true that in the opening montage, a bomber is seen with Silk Spectre's alias "Sally Jupiter" emblazoned on its side. Her real last name was Juspeczyk. She assumed the name Sally Jupiter because she did not wish to be known as being Polish. No one would be able to just look her up in the phone book so she did not really reveal her true identity.
The movie is set in an alternate history which diverged from ours in the 1930s. In many ways that reality is more advanced than ours, due to the inventiveness of Dr. Manhattan and other geniuses in the story. Most apparent anachronisms and factual errors in technology, design, fashion, music, communications, and other areas, cannot be counted as goofs for this reason.
When Dreiberg is in his secret basement with Jupiter, showing her the night-vision goggles he wore as Nite Owl, he turns the lights off while she's wearing them, and approaches her. His pupils are not dilated, like they should be in the dark.
If you watch the shadows on Dr. Manhattan carefully, it appears that the blue light is coming from an off-camera source, not his body. When he turns his head, the side of his face that is in shadow will change. When he is sitting on the bed holding the bra, the shadow of the bra on his chest indicates this as well. (Note: while Billy Crudup was emitting blue light from his motion capture suit during production, the computer model of Doctor Manhattan must be lit independently by animators.)
In Antarctica, as Rorschach and Nite Owl II slide open the doors when entering the facility, there are conduits and pipes on the right side of the screen that should continue through the wall but do not go anywhere. The sliding door passes through the wall where the pipes/conduits should be going. Also, the large pipe has a match outside but the perspective is not correct to have it meed up with the pipe from inside.
As the camera zooms out from the crime scene at The Comedian's apartment, the Chrysler Center is visible in the reflection of the glass, but is not visible as the camera zooms out far enough to be able to see where it should be.
After the fight between Veidt, Rorschach and Nite Owl II, Rorschach helps up Nite Owl as Veidt starts heading up the stairs. Rorschach had his hands at his sides, then the angle changed to over Veidt's shoulder and Rorschach's hands were inside his coat's pockets.
During the final battle in Adrian's Antarctic base, Laurie shoots Adrian with a pistol. It is hard to catch, but she takes this from a guard at Sing Sing during the breakout of Rorschach. Later it can be seen tucked away in her belt.
The particle accelerator is used to kill other characters, but why wouldn't they come back like Dr. Manhattan did? The other scientists had been killed by poison before being disintegrated. Dr. Manhattan was alive and conscious when he was disintegrated. His backstory also makes it explicit that he was taught how to recreate complex structures starting in his youth.
The American cities destroyed at the end are New York and Los Angeles, notably NOT Washington D.C., the seat of government. However, Moscow and Paris ARE destroyed. New York was shown to have not been destroyed entirely, thus it is reasonable to believe that the other cities were not destroyed entirely either, and the Soviet premier did survive to make peace.
When Rorschach is trapped in Edgar Jacobi's apartment, surrounded by SWAT teams, Jacobi's corpse blinks. However, recently deceased corpses will oftentimes show muscle reactions: twitches, gasps and flexing are not uncommon.
Veidt uses energy from Dr. Manhattan to destroy major cities across the world in order to end war. If he was able to do this, he might have been able to complete his original stated goal of creating renewable energy to end war. However, there is a big difference between using a physical process as a weapon, or as a useful energy source. In a real-life example, nuclear fusion was made into a weapon (a hydrogen bomb) in 1952, but despite all efforts, even 60 years later, the best fusion reactors are still too inefficient to be a practical energy source. So Veidt's original plan wasn't an option in the time frame he was given.
The New York blast's epicenter is Times Square, but the top-down view of the explosion is just a random 3D composite of various skyscraper models, including several slightly modified but recognizable buildings from lower Manhattan (e.g., 20 Exchange Place, 120 Broadway and 55 Wall Street).