Limiting the depth of field is an efficient way to bring the viewer's attention to the important part of the picture. Unfortunately it can be hard to adjust focus and aperture correctly in a fast moving scene, and many cheap cameras does not offer such possibilities at all. Out of focus blur is relatively simple to introduce after the picture has been taken, and Image Analyzer has a feature that can assist in the process.
The simplest way to introduce out of focus blur in a picture like the above is simply to make select the background and apply a smoothing filter to the selection, but this will introduce a hard visible edge against the non-blurred part of the scene. In this example the sand around the girls' feet should not be blurred but the sand near the audience should and we want a smooth transition from the foreground to the background.
In Image Analyzer's Out of focus blur dialog (Operations | Filters | Out of focus blur...) you can determine the vertical position of the focus and the size of the transition area.
Before opening the focus blur dialog you should select everything but the parts that should not be blurred at all.
Download source image
Download selection mask (Apply with Edit | Selection from image
Note: This feature is so far only available in the latest beta which you can get form the support forum. I hope to do the final release soon.