ImageIO will require the applet to be signed, and assumes client-side files. If the question is about loading files from the server, then see the LoadAGif example in http://faq.javaranch.com/java/CodeBarnApplets.
We can fix it! We just need some baling wire, some WD-40, a bit of duct tape and this tiny ad:
Gift giving made easy with the permaculture playing cards