What Attracts the Eye?
You probably want your photographs to have an impact on the viewer. But what attracts the viewer's eye may not be the same thing that attracted your eye.
You go out exploring with your camera. It's a beautiful day, and you're having a great time. Every now and then, something that looks like it would make a good photograph catches your eye, and you stop to examine it in detail. You carefully select a position to shoot from that gives you a good vantage point. You double check your focus and exposure settings so as to create the best shot you can. And only then you press the shutter release button. Using what you have learned, you do your best to get a good shot.
What was it that attracted your eye? Sometimes, it could be a species of wildflower or species of ground squirrel you haven't come across before. Sometimes, it could be the combination of more than one element, perhaps a small stream with those flowers and squirrel next to it. Sometimes, it could be the beautiful morning light, and that stream is basically just an excuse for something to put in the foreground with that light falling on it. Sometimes, you might not really be able to say what it was that caught your eye. It may just seem like a good shot, even if you can't fully articulate the reason why.
But even when you end up pleased with what you find and photograph, you may find that others don't share your excitement when they look at the resulting images. What caught your eye may not attract other people nearly as much as you might expect. Sometimes, it can seem as if other people just don't share your enthusiasm. What attracts the eye can easily differ between the photographer who was there on site and the viewer who has nothing to go on other than the resulting photos.
If you want a viewer to be attracted to your images and feel the way you feel about them, it's worth examining what it is that attracts their eye.
Photographs are flat, two-dimensional objects. They represent scenes from the real world, but they have important differences from it. When you're out with your camera and come across something that catches your eye, you can readily discern and identify objects you encounter. You may not know what species of flower you find, but you at least know it to be a flower. In addition to the fact that the world is three-dimensional, you have the added advantage of other sensory and contextual cues that present themselves together with what your eyes tell you about the world around you. When you look at a photograph though, all you can see is what lies within the frame. There is no context.
So if you are looking at a photograph, what is it you do see? What is it that attracts your eye?
One of the main attributes that tend to draw the attention of a viewer is focus. If an image has some areas in sharp focus and other areas that are less sharp, the eye generally is drawn to the areas in focus. If the autofocus on your camera focuses on a tree immediately behind your subject rather than the subject itself, a viewer will at best be confused as to what the intended subject is. In order for them to focus on what you want them to, your camera needs to be focuses on it when you shoot. Sometimes landscape photographers shoot so as to have the depth of field extend equally from foreground to background to capture a sense of place as well as the majesty of the vista as a whole. Such images can work well so long as the subject is the vista rather than some object within it. If you want to call attention to something in particular, try to make that obvious in how and where you focus.
Contrast can also play a major role in what a viewer tends to look at in an image. Specifically, the eye is drawn to bright areas within an overall dark frame, or to significantly dark areas within an otherwise light frame. In an average image, any bright, highlight areas will appear to be the subject, at least initially. If you don't intend those areas to be the subject, then why have them compete with it? Specular highlights can be light magnets, pulling the eye back to them even once the viewer identifies other objects in the frame deserving of notice.
Saturation and color can serve as queues as well. Just as differences in brightness, differences in color intensity often serve as queues for viewers looking at an image. Whatever stands out will thus contribute to defining the subject in the eye of the viewer. Warm colors such as yellow and red tend to draw the eye too. Generally speaking, warm colors appear to pop out while cool colors such as blue and green often seem to recede in importance. A saturated, warm color serves as an exceptionally strong cue to attract attention.
Recognizable people and animals to attract the viewer's eye too, especially when their eyes are visible. Perhaps because we instinctively want to know if those eyes belong to friend or foe, a viewer will be drawn to those eye. If it seems that those eyes are looking at something, whether it be on the other side of the frame or an implied something lying outside our field of view, we will naturally be curious. We want to know what it is they are looking at. It naturally becomes important to us.
An object that breaks the frame will seem important too, even if unduly so. Even a small rock or other object of sufficient contrast that likes partially in the frame and partially out of it will cause the eyes to stop for a moment as they scan the frame. That object prevents the eyes from naturally scanning the frame. Attention will be drawn to this point time and again, even when the viewer has determined that there's nothing there that really deserves that focus. It may an insignificant object, but it comes to have undo visual weight simply by virtue of its location, cutting through the edge of the frame. If there are any such potential distractions, the camera frame should be oriented so as to crop them out completely, or to ensure they lie completely inside the frame.
This can't be considered a comprehensive list of course, but it can hopefully serve as a quick checklist to make sure the viewer's eye is attracted to what you want them to look at. Remember that whatever it was that attracted your eye and caused you to shoot an image may not be what the viewer's eye is naturally drawn to when they look at that image. It's up to you to take steps to have these factors reinforce your intended subject, not compete with it.