"""Draw on top of an image"""

from Tkinter import *

import sys

def main():

    filename = sys.argv[1]

    root = Tk()

    img = PhotoImage(file=filename)

    w, h = img.width(), img.height()

    canv = Canvas(root, width=w, height=h)

    canv.create_image(0, 0, anchor=NW, image=img)

    canv.pack()

    canv.bind('<Button-1>', blob)

    root.mainloop()

def blob(event):

    x, y = event.x, event.y

    canv = event.widget

    r = 5

    canv.create_oval(x-r, y-r, x+r, y+r, fill='red', outline="")

main()