There are plenty of 'rules' for good photos. Of lighting, color and composition, of getting the technicalities right. Of patterns and lines and gestures and expression and simplicity and structure. Elements that can help to elevate an image, to guide the eye of the viewer to the subject, or create the intended mood.
I'll look more at those in future posts, but for now lets aim really high and look at the greats. What elevates an image to being exceptional or iconic?
Does a great photograph have to be beautiful? I think that there does have to be an element of beauty, whether it is purely aesthetic or in relation to the story or implications of the image. Of course this leads to a potential dilemma of whether beauty is universal or whether it is an assessment of the viewer and their worldview and values or the prevailing culture of the time. I believe that there is some beauty that is universal, that a dramatic sunset or a majestic creature holds an intrinsic beauty. But I also believe that an image that appears beautiful to one person may not appeal to another. It should be still possible though to acknowledge a great image, even if I don't personally find it appealing.
Here is the personal and emotional element. A great image should cause an emotional response. Perhaps not from everybody, but from many. That might be a response to the content, the story, the subject, or the visual elements. It could be humor or pain, or it could be a mood that sucks you into the world of the image.
A great photo doesn't have to be surprising, but many are. It might be a humorous element in a street scene or a shocking image of war or a new discovery or new perspective on something familiar. The problem here though is that the element of surprise might change over time. Other photographers start to produce similar images, it becomes more familiar. The original might have lost it's ability to surprise but it may still remain iconic. It's greatness is bound up in what it communicated at the time and remains great because of it's place in history.
It could also be a quirkiness. It might break some of the 'rules' that I mentioned for a good photo, intentionally going against accepted theories. It could be a twist to an established genre, an unexpected element to an image that makes it stand out. For example, Annie Leibovitz decided to photograph Whoopi Goldberg in a bath of milk. It was bold, unusual (at the time, now much copied), memorable, and also raised plenty of questions (another great quality for a strong image).
This is all considering a great photo in terms of how it is perceived by the world, but maybe there's something equally important and more attainable that we can aim for. Maybe the great photo for you right now is whether you tried something new. Or you took the best photo that you've ever taken of your son or partner or friend. Maybe you took your first street portrait, or a photo that's better than the photos you took yesterday or last week or last year. You're moving forward, still creating, and making better art.
And when you see an image that you love, that truly resonates with you, take time to enjoy it. Think about why you like it so much. What works, what draws you to it or causes that response? I'm not suggesting you copy it, although that can still be a useful exercise (even the Beatles were originally a cover band). But it might just help you to work out what you want to say and show in your own photography.
(If you want a starting point, I have various collections from great photographers on my Pinterest page here.)