Horizontal photographs are photographs that are wider than they are tall. Vertical photographs are photographs that are taller than they are wide. Cameras are designed to take one type of photograph -- horizontal. This follows the way that human beings see the world. Our eyes are set horizontally across from each other, giving us a view that is wider instead of taller.
This allows us to be more aware of our surroundings through peripheral vision. In photographs, our vision is limited by the edges of the frame so that peripheral vision is eliminated. Having no peripheral vision in photography helps the photographer to focus attention on the intended subject by limiting the field of vision.
Since a photograph cannot selectively focus once taken, this limitation of the field of vision is extremely important. By turning a camera sideways, photographers achieve a vertical photograph and further limit the field of vision.
When to Use Horizontal Photographs
Horizontal photographs are the most common photographic orientation because the camera is designed to take photographs this way. Many photographers do not think to turn the camera sideways to take a vertical image. Horizontal images have some distinct properties.
Horizontal images are best used...
When the subject is horizontal: When your subject is wider than it is tall, a horizontal image compliments the subject.
To allow the subject to move horizontally: When your subject is moving from one side of the frame to the other, using a horizontal format in conjunction with the rule of thirds visually allows the subject room to continue moving. This will amplify the sense of motion in the image. This is also true of subjects looking to the side. Having open space to the side allows the subject's gaze to continue farther than is possible in a vertical image.
To convey a sense of space: Horizontal images can be used to suggest a sense of largeness in landscapes. If a small subject is placed in a large field, it can also be used to suggest loneliness.
When to Use Vertical Photographs
Vertical photographs are less common than horizontal photographs because they require the photographer to take the extra step of turning the camera sideways. Many photographers do not think to turn the camera sideways to take a vertical image. Vertical images are a photographer's way of attempted to imitate the brain's natural selective focus ability.
Vertical images are best used...
When the subject is vertical: When your subject is taller than it is wide, a vertical image compliments the subject.
To allow the subject to move vertically: When your subject is moving up or down, using a vertical format in conjunction with the rule of thirds visually allows the subject room to continue moving. This will amplify the sense of motion in the image. This is also true of subjects looking up or down. Having open space to the top of bottom allows the subject's gaze to continue farther than is possible in a horizontal image. Remember also that when a subject is moving deeper into an image or moving towards the camera that this appears as "up or down" movement when converted into a 2D image. This is why many leading lines images work very well as vertical images.
To focus attention: Vertical images can be used to focus a viewer's attention on a single subject by removing almost all sense of peripheral vision. This is the theory behind portraits and other single-object compositions.