You might not have included the image file in the icons directory.
Thanks for this but this is not the issue that I am facing. I am able to see the custom work items in this editor. I can not see cusom work items with the new editor provided by codehoop which is based on graphiti, the one that you can download from http://codehoop.com/bpmn2
I did not try this editor and I am not if there is an issue.
But, before that did try copying the configuration files to META-INF directory and image to icons directory with the CLASSPATH of the codehoop web application?