Console looks for a ${processid}-image.png file to use as your image of your process. You can create this image in eclipse (see for example video http://people.redhat.com/kverlaen/jBPM5-guvnor-integration.swf) or if you are using only Guvnor with the Oryx designer, see http://vimeo.com/26126678.
Hope this helps.