when I run the code within Eclipse Plattform the Image is shown. Now I signed the created jar archive, but when i run on the embedded server no image is shown.
Is the image file in the JAR? It should be. Check out the Java Tutorial chapter on How to use Icons. You can't just use a file name to create a JImageIcon because the contents of a JAR don't show up in the file system. The tutorial shows you how to get around that problem.