Use images in tooltips : JToolTip « Swing « Java Tutorial

import javax.swing.JFrame;
import javax.swing.JLabel;

public class Main {

  public static void main(String[] args) {

    JFrame frame = new JFrame();
    JLabel label = new JLabel("Label with image in Tooltip!");
    label.setToolTipText("<html><img src=\"" + Main.class.getResource("tooltip.gif")
        + "\"> Tooltip ");
    label.setHorizontalAlignment(JLabel.CENTER);
    frame.setContentPane(label);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setBounds(100, 100, 200, 100);
    frame.setVisible(true);

  }
}

14.72.JToolTip
	14.72.1.	Adding JToolTip to component
	14.72.2.	Creating HTML 3.2 formatted text tooltip: the text string begins with 'html' in any case
	14.72.3.	Creating Customized JToolTip Objects: customize and override its inherited public JToolTip createToolTip()
	14.72.4.	Displaying Positional Tooltip Text: display different tooltip depending on the mouse pointer's location
	14.72.5.	Displaying Mnemonics in tooltip text
	14.72.6.	Label with tooltip
	14.72.7.	Use images in tooltips
	14.72.8.	Make a tool tips appear immediately
	14.72.9.	Use the default tool tip location
	14.72.10.	Setting the Location of a Tool Tip
	14.72.11.	Enabling and Disabling Tool Tips
	14.72.12.	Showing an Image in a Tool Tip
	14.72.13.	Italicize the second line
	14.72.14.	By default, the lines are left justified. Center the lines.
	14.72.15.	Showing Multiple Lines in a Tool Tip
	14.72.16.	Disable / enable application tool tips
	14.72.17.	Making Tool Tips Remain Visible
	14.72.18.	Set the location of the tool tip such that its nw corner coincides with the bottom center of the button
	14.72.19.	Modify the behaviour of the default JToolTip
	14.72.20.	Customizing a JToolTip Look and Feel