What makes a shot iconic?

** SPOILERS AHEAD **

There are many things that can become iconic about a certain film. It could be the music, such as in Jaws (1975) or Star Wars (1977), or it could be an iconic piece of dialogue. These might include famous lines like 'I love the smell of napalm in the morning' (Apocalypse Now, 1979) or 'Good Morning Vietnam' (Good Morning Vietnam, 1987). Films themselves can be iconic for these reasons and many others, including their cultural impact (Battleship Potemkin and its Soviet Union propaganda), their impact on film (Citizen Kane for umpteen reasons, including camerawork, lighting, etc) or if they had an impact on the viewer (La La Land for me personally).

However, one other thing that sustains itself throughout film and goes into many other forms of media is shots itself. Anybody can name an iconic shot, from E.T. flying through the sky, in front of a moon or James Bond in the eye of a gun barrel. There are many reasons towards what might make a shot iconic because it is almost a mystery. Iconic shots seem to randomly pop up in today's culture and most people accept them for what they are, without fully appreciating why they are iconic.
It would be impossible to dissect every single iconic shot within cinema so I am going to list some reasons for why a shot could be iconic. This list will almost definitely not be exhaustive; however, hopefully it will sum up a large majority of reasons.

1) Its impact from within the context of the film

Some shots become iconic because of what effect they have on the film itself. This would link into the notion of plot lines. For example, one of the last shots of The Shawshank Redemption (1994), we see Andy on his knees, in the pouring rain, tasting his first breath of freedom in many years. Many films have done this kind of shot for example when Gale and Evelle escape prison in Raising Arizona (1987). But this isn't particularly iconic - which begs the question, why is the former shot so much more iconic.
First of all, we must look at it in terms of where it comes in the film - at the very end. The film has followed Andy's entire journey through prison, seeing his friendship develop with Red, his fights and his rebellious acts. At the very end, he has battled through all his trials and tribulations, and has ultimately outwitted the prison by escaping, something the other inmates only dreamed of doing. His freedom means a whole lot more to the audience than it does in Raising Arizona. 

Their escape is simply a plot point, which appears briefly into the film. They are unknown to the audience at this point - we do not know if they are good, bad, or crazy. It ironically turns out they are friends of Hi McDunnough and they escaped due to greed. There was no previous character development for them and they end up returning to the prison anyway.
With Andy, his character has been built up and the audience knows him almost inside and out. He never deserved to go into prison in the first place so the notion of him escaping means that he has won what he deserved and the protagonist has achieved victory. In Raising Arizona, these men were already convicted criminals. 

This shot is iconic because it reminds audiences of this film and what the plot is. It gives them fond memories of how the protagonist ended up winning against the prison life.

Of course there are many more films which could argue that their shots are iconic in terms of their context from within the film. Some of these may include, but are certainly not limited to, the last shot of Fight Club (1999), the four friends skipping along the yellow brick road towards Oz in The Wizard of Oz (1939) and the kiss between Peter Parker (disguised as Spider-Man) and Mary Jane in Spiderman (2002).

2) The shots' impact on filmmaking

Many shots have gone on the change how film is viewed and made. This might be how significant it may have been for camera technique, practical or digital effects, and/or anything to do with mise-en-scène (costumes, lighting, settings, props, acting). Citizen Kane is well known to have such an influence on filmmaking, with some camera work that had never been thought possible and some camera techniques which have since become normal within the film industry,

For this section though, Psycho's shower scene is significant in many ways. Made in 1960, Hitchcock completely defied audience expectations by having the protagonist killed off barely 1/3 of the way into the film. This scene has since become one of the most iconic character deaths, if not one of the most iconic scenes ever conceived in cinema history.

Marion Crane is taking a shower and unbeknownst to her, a silhouette of Mother slowly approaches the curtain, only to come and stab her to death. Hitchcock managed to film all this without showing the knife piercing the skin, nor by showing any nudity whatsoever. Overall, the shower scene in Psycho required 78 shot set-ups and took seven days to film. The set was built so that any of the walls could be removed, allowing the camera to get in close from every angle. Although other scenes were shot with more than one camera, this one used only one cameraman. These statistics alone show how much work was put in to making this scene. Obviously, this shot would easily fit into category 1) of this list, but in terms of how it was filmed, how it effected plot points within films (directors happily kill off protagonists in movies now, such as in Fellowship of the Ring and Star Wars: The Force Awakens) and showing how an incredibly high budget is not required to shoot a spectacular scene. This scene is also iconic for how terrifying it is, with the screeching soundtrack, to the black-and-white colour palette, and how it attacks a vulnerability everybody can relate to.

3) The shots cultural impact

Some shots have become synonymous with a film or a style of film. This doesn't necessary link in with the films' plot development or a film's technique. It means that once somebody sees a shot, it instantly links in their to a certain film. It can be as subtle as a red light (HAL) in 2001: A Space Odyssey (1968) or something as huge as the Imperial Star Destroyer at the beginning of Star Wars (1977). Some shots have, unfortunately, lost their link with film and have become synonymous with pop culture instead. People may still know that it is linked to a film, but it has been used so much, it is completely iconic in more ways than just the film. For example, Reservoir Dogs (1992) shot of the fight between Mr White and Mr Pink - this kind of shot is mimicked in so many different areas of media (and knowing Quentin Tarantino, it may well have been copied from another film).

4) The shots impact on the audience

Some shots have had an emotional impact on the audience, be it fear, laughter, sadness, etc. The classic 'Here's Johnny!' shot in The Shining (1980) invokes a sense of fear as Jack tries to get to terrified, trapped Wendy. The dance sequence in La La Land (2017) where Mia and Sebastian cross arms indicates their developing love interest. The shot of Roger Thornhill running away from the airplane gives the audience a sense of suspense. Charlie Chaplin sliding through giant cogs in Modern Times (1936) is funny and makes audiences laugh at its absurdity. Scarface's (1983) 'Say hello to my little friend' shot invokes excitement and thrills. There are hundreds of these shots which may link in with all three previous points, but may be most iconic for the emotion it evokes.

For all of these points, there are likely hundreds of more examples that haven't been chosen. However, this is done simply to try and dissect the notion of what makes a film shot iconic. There may also be other ways that a shot might be iconic, but these are likely the most frequent.