Different Types of Blurs
You wouldn't think that there would be a variety of blurs to choose from, but there are. Photographers are so crazy about blur that they have a special word to describe the quality of the out-of-focus areas of a photograph: bokeh. Some photographs can spend all day talking about it. Your image-manipulation program likely will have three kinds of blurs (and then maybe some fancy add-on blurs): a basic blur, a Gaussian blur, and a motion blur. Blur filters work by creating intermediary colors to soften the edges of color transitions. A Gaussian blur is simply a particular mathematical algorithm used for creating a type of blur. It's named after the German mathematician Karl Fredrich Gauss; it's probably not any better or worse than your ordinary blur filter, but it's very popular. A motion blur filter creates a directional blur to imitate the effect you would get if an object was moving rapidly in front of your camera.
The most useful place to use a motion blur is, obviously, when you want to suggest motion. The motion blur in Figure 5 makes it look as though the guitar player is lurching toward you, which isn't necessarily bad because it turns the static photo into an action shot and brings the product label to the forefront.
Figure 5 With a motion blur added, the subject appears to be moving toward you.