This is a simple method for image editing.
We can defuse the background to draw attention to the subject. We can simulate the defocused Depth-of-field digitally. This tutorial illustrates a simple process of doing this in Photoshop, Photoplus or GIMP. For this tutorial, I use a photo taken at a Expo in Nagoya, Japan.
In the above photo, the background is fairly sharp. We will like to defocus it to direct more attention to the 3 shark men in blue.
Firstly, using the Polygonal Lasso, select the areas outside of the 3 shark men. I leave a small border gap between the subjects and the background.
Next, I select feather to soften the edges of the selection. See the photograph directly below.
Next, I apply the Gaussian Blur. See the result below.
Now, we can see that the image is more impactful as attention is focused more on the subject now.
Depth of field is not limited to the domain of photography. Even many capable 3D software programs can stimulate DOF using the camera settings. 3D programs such as Carrara, Yafaray, V-ray have options for stimulating DOF.
Again, this should be applicable to most decent graphic and image editors.