Image « LineChart « JFreeChart Q&A

2. Line Chart with customizable image symbols

You can set the shapes in the renderer, but images are more difficult. There is some support in StandardXYItemRenderer to display images - to use it, you need to subclass the renderer, and override the getImage() method to supply the image(s) to display. It's pretty old code, and I don't know if anyone uses it or even if it works.