Tkinter/PIL, How to Drag and Drop the image with mouse?

[BirdaoGwra]

Hi,
I hv created an application with Tkinter/PIL in python25. It can import an image into the canvas. Now could someone kindly tell me how to select and move that image with mouse? Any help would be really appreciated.

# BirdaoGwra 
# January 25, 2010
 
import sys, os, math
 
from Tkinter import *
import Tkinter as tk
import tkFileDialog as tkfd
import tkMessageBox as tkmb
 
import PIL as pil
from PIL import Image, ImageTk
 
myFormats = [
        ('Windows Bitmap', '*.bmp'),
        ('Portable Network Graphics', '*.png'),
        ('JPEG/JFIF', '*.jpg'),
        ('CompuServe GIF', '*.gif'),
        ('All File', '*.*')
        ]
 
class MyApp(object):
    def __init__(self, master):
        frame = tk.Frame(master)
        frame.pack()
 
        self.canvas = tk.Canvas(width=520, height=350)
        self.canvas.pack()
        self.canvas.config(borderwidth=1, bg='black')
 
        # Create the menubar
        menu = tk.Menu(master)
        root.config(menu=menu)
        # File menu
        filemenu = tk.Menu(menu, tearoff=0)
        menu.add_cascade(label="File", menu=filemenu)
        filemenu.add_command(label="New          Ctrl+N", command=self.new_file)
        filemenu.add_command(label="Open...      Ctrl+O", command=self.file_open)
        filemenu.add_separator()
        filemenu.add_command(label="Save...      Ctrl+S")
        filemenu.add_command(label="Save As...   Ctrl+Shift+S", command=self.file_saveas)
        filemenu.add_separator()
        filemenu.add_command(label="Exit         Ctrl+Q", command=self.do_exit)
 
    def new_file(self):
        """create a new document"""
        self.canvas.delete(ALL)
        # self = tkmb.showinfo("Birdao Anime!", "Yet to implement!")
 
    def file_open(self):
        """open a file to read"""
        # self.canvas.delete(ALL)
        filename = tkfd.askopenfilename(filetypes=myFormats)
        if filename != '':
            im = Image.open(filename)
            if im.mode != "RGBA":
                im = Image.open(filename).convert("RGBA")
                source = im.split()
                R, G, B, A = 0, 1, 2, 3
                mask = im.point(lambda i: i> 0 and 255)
                source[A].paste(mask)
                im = Image.merge(im.mode, source)
 
        self.graphic = ImageTk.PhotoImage(image=im)
        self.canvas.create_image(100,100, image=self.graphic)
 
    def file_saveas(self):
        """get a file name and save it"""
        # no default file
        filename = tkfd.asksaveasfile(filetypes=myFormats)
        if filename:
            self.saveimage.save(filename)
 
    def do_exit(self):
        root.destroy()
 
root = tk.Tk()
root.title("Birdao Anime 0.1")
root.config(bg='gray')
 
# use width x height + x_offset + y_offset (no spaces!)
root.geometry("%dx%d+%d+%d" % (640, 480, 120, 80))
myapp = MyApp(root)
root.mainloop()

And also how to center the canvas?

Thanks in advance
Regards