If the image is not under your webapp's directory structure, you'll need to write a
servlet that streams the image to the browser.
This is not difficult.
I have an example app that does this.
http://simple.souther.us Look for SimpleStream.
In that app, I'm using getResourceAsStream to read image files under the webapp's directory structure but hidden from the web under WEB-INF.
In your case, you will have to use java.io.FileReader to read your image files but, otherwise, everything should be the same.