Camera shake is the unintentional blurring of an image, usually because the shutter speed is too low. In this image the blur was intentional to give the effect of a moving vehicle, however usually the image should be sharp. Camera shake can be prevented by using a shutter speed close to the focal length of the lens when handheld, for example with a 30mm lens a minimum of 1/30th second shutter speed should be used. Camera shake and intentional movement in images (you may see this refered to as Intentional Camera Movement or ICM) can be used to create interesting and unusual images.
