random textimage

[gert]

import string
import random
import PIL
from PIL import Image, ImageFont, ImageDraw
from PIL import ImageEnhance, ImageOps, ImageStat
from StringIO import StringIO
import os

pwd = os.path.dirname(os.path.abspath(__file__))
fpath=os.path.join(pwd,'img.ttf')
iname=os.path.join(pwd,'pass.jpg')

def gen():
    text = str(random.randint(0,1000))
    im = Image.new("RGB", (125, 34), "#fff")
    ttf = ImageFont.truetype(fpath, 16)
    draw = ImageDraw.Draw(im)
    draw.text((10,10), text, font=ttf, fill="green")
    img = StringIO()
    im.save(img, "JPEG")
    f = open(iname)
    f.write(im)
    f.close()
    return text

if __name__ == "__main__":
    print gen()

gert at gert:~/Desktop/svn/xhtml$ python2.5 textimg.py
Traceback (most recent call last):
  File "textimg.py", line 27, in <module>
    print gen()
  File "textimg.py", line 22, in gen
    f.write(im)
TypeError: argument 1 must be string or read-only character buffer,
not instance
gert at gert:~/Desktop/svn/xhtml$

i am stuck anybody can help me ?