Have you actually set the bump strength to 100%, and made sure the min and max values are sensible - remember they are in cm, so work out how big the bumps would need to be to be right on the size of plane you are using. You also need directional light - if you just look dead on at teh surface, with no lights beyond the basic one from the camera, then there won't be much to see. In any event, making a bump map from the image isn't going to do a great deal in most cases - you want the map to be light where the surface is raised and dark where it's depressed.