I would do something along this lines to achieve this:
On the JSP page you put a link to an image:
the rest
This link points to your servlet, it generates image using request parameters, you do not need to save it, just put it right into response's output stream. You have to remember to disable browser caching for this servlet.
JSP page is displayed first, next all the images are requested, it should work just fine.
Of course, you should not put the text to display in a parameter like this, you should propably encipher it somehow or store it in a HTTP session.
Hope this helps.
