matplotlib save issue

import wx
from matplotlib.figure import Figure
from matplotlib.backends.backend_wxagg import FigureCanvasWxAgg
import Image

class Test(wx.Frame):
    def __init__(self):
        img = Image.open('stinkbug.png')
        wx.Frame.__init__(self, None, -1, 'Line save issue',size=img.size)

        self.create_menu()

        self.scroll = wx.ScrolledWindow(self, -1)
        self.scroll.SetScrollbars(5,5,600,400)

        x, y = img.size
        self.figure = Figure(figsize=(x/72.0, y/72.0), dpi=72)
        self.canvas = FigureCanvasWxAgg(self.scroll, -1, self.figure)
        self.canvas.SetBackgroundColour('grey')
        self.axes = self.figure.add_axes([0.0, 0.0, 1.0, 1.0])
        self.axes.set_axis_off()
        self.axes.imshow(img, aspect='auto')

        self.canvas.draw()
        self.background = self.canvas.copy_from_bbox(self.axes.bbox)
        self.canvas.restore_region(self.background)
        line, = self.axes.plot([5, 100], [5, 100], c='#00FF00',
                               marker='-', zorder=1,
                               animated=True)
        self.axes.draw_artist(line)
        self.canvas.blit(self.axes.bbox)

    def create_menu(self):
        self.menubar = wx.MenuBar()

        menu_file = wx.Menu()
        m_save = menu_file.Append(-1, "&Save", "Save")
        self.Bind(wx.EVT_MENU, self.on_save, m_save)
        menu_file.AppendSeparator()
        m_exit = menu_file.Append(-1, "E&xit\tCtrl-X", "Exit")
        self.Bind(wx.EVT_MENU, self.on_exit, m_exit)

        self.menubar.Append(menu_file, "&File")
        self.SetMenuBar(self.menubar)

    def on_save(self, event):
        self.figure.savefig(r'C:\Documents and Settings\achilds\Desktop\out.png', dpi=self.figure.dpi)

    def on_exit(self, event):
        self.Destroy()

if __name__ == '__main__':
    app = wx.PySimpleApp()
    frame =  Test()
    frame.Show()
    app.MainLoop()