Where is this code located - in a JSP page? I'm guessing it is, since you are posting to the JSP forum. A JSP page really can't (and shouldn't) use the output stream. If the response consists of an image you need move this code to a servlet.
Ping & DNS - updated with new look and Ping home screen widget
JSP compilers will often add characters to the output stream going to the browser. Since the primary intent for JSP is textual output (Mainly HTML or XML) these characters aren't a problem. If you're trying to write binary data to a browser, however, they will become a problem. This is why it's best to do this with a servlet.
Thanks folks ,I used a servlet and it worked well. The code i earlier tried was straight from the myfaces example i downloaded from Myfaces. its contained in the file_upload.java file and it used a JSP to emit images which is wrong like you two gentlemen pointed out and this i agree with