Using the jfreechart plugin. You can select PNG or JPEG image - but the HTML response sends HTML content type
e.g. in my app
Content-Type: text/html; charset=iso-8859-1
This works if you use an <img src="..:"/> tag - but a direct call to the image URL returns the image as text to the browser.
(BTW - not sure why there are several plugin components in this JIRA but not one for the chart plugin or for plugin: other)