CGI to make PNG image

[Take Sato]

I made a simple CGI script to return images on WinNT with Apache1.3.12.

It works all right to return JPEG,GIF,BMP images,
but not with PNG.
(IE5.0 and NS4.5 cannot understand it as correct image)

I don't know what's wrong with it.
Can anyone help me ?

-----------------------------
import Image
try:
    import msvcrt,os  #set standard output to binary mode
    msvcrt.setmode(sys.stdout.fileno(),os.O_BINARY)
except: pass

im=Image.open("foo1.jpg")

... # some operation

print "Content-type: image/png"
print
im.save(sys.stdout,"png")

#NOTE! above script works fine if it's like following,
# (once saved as file and reopened.)
print "Content-type: image/png"
print
im.save("foo2.png","png")
print open("foo2.png","rb").read()