Efecto seleccion de rectangular con el mouse / Select images by using a rectangular area. NOTA: Si se pone una imagen como fondo en el jpanel + un listener mouseDragged, se podra obtener la seleccion de una porcion de la imagen. Fuente: http://www.daniweb.com/software-development/java/threads/342036/how-to-select-images-by-using-a-rectangular-area…

SelectionDemo.java

import java.awt.BorderLayout;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Point;
import java.awt.Rectangle;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.event.MouseMotionListener;
import javax.swing.JPanel;

public class SelectionDemo extends javax.swing.JFrame {

    public SelectionDemo() {
        initComponents();
        add(new DrawingPanel(),BorderLayout.CENTER);
        setSize(500,500);
    }

    class DrawingPanel extends JPanel implements MouseMotionListener, MouseListener{

        Rectangle selection;
        Point anchor;

        public DrawingPanel(){
            addMouseListener(this);
            addMouseMotionListener(this);
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            if (selection!=null){
                Graphics2D g2d = (Graphics2D)g;
                g2d.draw(selection);
            }
        }

        public void mousePressed(MouseEvent e) {
            anchor = e.getPoint();
            selection = new Rectangle(anchor);
        }

        public void mouseDragged(MouseEvent e) {
            selection.setBounds( (int)Math.min(anchor.x,e.getX()), (int)Math.min(anchor.y,e.getY()),
                    (int)Math.abs(e.getX()-anchor.x), (int)Math.abs(e.getY()-anchor.y));
            repaint();
        }

        public void mouseReleased(MouseEvent e) {
            selection = null;
            repaint();
        }

        // unused
        public void mouseMoved(MouseEvent e) {}
        public void mouseClicked(MouseEvent e) {}
        public void mouseEntered(MouseEvent e) {}
        public void mouseExited(MouseEvent e) {}
    }

    private void initComponents() {
        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
        pack();
    }

    public static void main(String args[]) {
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                new SelectionDemo().setVisible(true);
            }
        });
    }
}