One usually tries to compose the elements of a photograph in a pleasing and interesting way. Often one tries to utilize certain rule or style that has been verified to work. Picture composition can be approached also from another perspective. When composing a photo one can think about things that should be avoided in the composition. Once the good composition has been found, one should check certain things that can generally speaking be considered as mistakes in image composition.

Distractions on the Edge
Always when composing a photograph one should observe the edges of the frame and look for elements that might be distracting and steal attention from the subject itself. Picture 1 is an example of this kind of situation. The feet of the chair in the upper right corner stand out well. They steal some attention from the cat and lead the eye of the viewer away from the photo. Picture 2 is fixed version of the same photo. Picture 2 is cleaner and the eye of the viewer stays better inside of the photograph.

Picture 1. Photo above is clean otherwise but the chair feet in the top right corner are distracting and steal attention from the subject itself.

Picture 2. Without the chair feet the photo is cleaner and the subject gets more attention.

Mergers
One should always pay attention to the background of the photographed subject. Sometimes there are elements behind the subject that merge with the subject like in the picture 3. The wing of the butterfly and the flower in the background overlap as if forming one unity. Better way to compose the butterfly is to find cleaner a background for it like in the picture 4. In picture 4 the wing doesn't merge with the background and the form of the subject stands out more. While composing a subject one should ask the following questions:

Does the subject merge with the background?
Is the contrast between the subject and the background strong enough so that the subject stands out?
Does the subject look good on the chosen background?
One way to separate subject and background is the use of complementary colors. Complementary colors are well distinguishable from each other and strengthen each other. Another method to emphasize the subject is to use textures. A subject with complicated texture stands out well from background with simple texture. A subject with simple texture stands out well from background with complicated texture.

Picture 3. In the photo above the upper part of the butterfly wing merges with the flower in the background. Because of that the butterfly doesn't come up as well as possible.

Picture 4. In this photo the butterfly is completely on the blue background and stands up well from the background.

Both these photos are bad, but at least the one on the right doesn't have a tree growing out of the subjects head.

When we cut people in half or trim their heads or feet, we've committed a border merger. This is often caused by poor alignment of the photographer's eye in the camera viewfinder. To avoid border mergers, line your eye up squarely behind the viewfinder and adjust the picture format to leave a little space around everyone. If you must crop out a portion of the subjects body do not crop them at a joint in their body. This will lead to an amputated feeling in the image. Instead of cropping at the ankle crop at the calf, instead of cropping them at their knees, crop at their thighs.

An example of a border merger.

Near mergers may not be quite as objectionable, but they can steal attention from your center of interest. Near mergers are objects or lines that are just too close to the principal subject.

In this image the ball and umbrella tip are near mergers.

Kissing Edges in Photographs
In picture 5 the horizon and the upper edge of the subject are exactly in the same line. These kind of kissing edges should usually be avoided by placing the edges to different locations. The situation in picture 6 is better. In picture 6 the horizon is clearly upper than the edge of the subject. Also situations where edges of the subject kiss the edges of the photo should usually be avoided.

Picture 5. In the photo above the horizon is in the same line with the edge of the subject. These kind of kissing edges should usually be avoided.

Picture 6. In this photo the horizon is clearly upper than the edge of the subject. The photo is cleaner and easier to look at.

Avoiding Mistakes
The mistakes mentioned above can be avoided and removed in several ways. The first step is to pay attention to these things when taking a photograph. When the possible mistakes are known they can be removed by using the following methods:

1. Change the Angle
The easiest way to remove the mistakes mentioned above is to change the angle. One can often avoid these mistakes with a slight change in camera angle. The subject can be photographed for example from another direction or from another distance.

2. Modify the Scene
Sometimes mistakes can be avoided by modifying the scene. What I mean is that, for example in the situation of picture 1 the chair could possibly have been replaced before taking the photo. Of course there would have been a risk because the cat might have moved away.

3. Use Digital Image Processing
Also digital image processing (Photoshop) can be used to remove the mistakes mentioned above. The photo can be cropped or it can be modified for example by using the Clone Stamp tool.

By knowing the possible mistakes beforehand one can avoid them. . . .
Or one could use them to create interesting and comical images.