I had the same question recently and jonlee came to my rescue so I thought I'd pass his wisdom on to you filtered throught my inconherency ...
Create a directory named uploads.war (or whatever name you want, just make sure the directory has a .war extension) in your deploy directory. Create a WEB-INF directory with a jboss-web.xml file that defines the context. Then from your "real" application upload the graphic files to /usr/jboss/server/default/deploy/upload.war, either hard code the location or use an initparm to the servlet. To read the files from your app use http://www.mydomain.com/uploads/filename.gif. That works well and is an interesting way of serving static content with JBoss/Tomcat.
Another solution was a lot more work for me to get going. I configured Apache to use Tomcat as a jsp container so I could then just put and get my graphics from docroot. The downside is Apache handing off requests to T
omcat so there is some time penalty involved, but I'm not sure how much yet.
Well, the upload.war solution is definitely good. At least somebody who helps me to solve my uploads pain. ;))