I am certainly no art historian, but I think this thread is mixing two different things, blur and impressionism. Someone who knows more about art can chime in if I am wrong. Impressionist paints are not exactly blurry. If you stand close enough, you can clearly see discrete paint strokes.
David--if you just want to introduce blur, there are lots of ways to do it. A common one is the Orton method. The simplest way to do this is to duplicate the image as a new layer in a program like photoshop. then add blur to the top layer and blend them. I'll post below a similar image to the one above that was 'ortonized' this way. It's not a good example--I did no editing at all other than a quick blur-and-blend--but it shows what I am talking about.