I have taken the rt.jar from my jdk installation and deployed it as a bundle into the ESB. I don't know if this is the recommended approach but it has certainly solved the problem for now.
No, don't install rt.jar as bundle.
You can let system bundle 0 export this package.
You can edit $FUSE_ESB/etc/jre.properties, add com.sun.image.codec.jpeg to the jre-1.6 property(I assume you're using JDK1.6)
Thanks a lot mr. Freeman!, that worked much better :-D