Python: Check if uploaded file is jpg

...
incomming_image = self.request.get("img")
image = db.Blob(incomming_image)
...

Start Marker  | JFIF Marker | Header Length | Identifier
0xff, 0xd8    | 0xff, 0xe0  |    2-bytes    | "JFIF"

def is_jpg(filename):
    data = open(filename,'rb').read(11)
    if data[:4] != 'xffxd8xffxe0': return False
    if data[6:] != 'JFIF': return False
    return True

from PIL import Image
def is_jpg(filename):
    try:
        i=Image.open(filename)
        return i.format =='JPEG'
    except IOError:
        return False

import imghdr

image_type = imghdr.what(filename)
if not image_type:
    print "error"
else:
    print image_type

image_type = imghdr.what(filename, incomming_image)

${h.form(h.url_for(action="save_image"), multipart=True)}
Upload file: ${h.file("upload_file")} <br />
${h.submit("Submit", "Submit")}
${h.end_form()}

def save_image(self):
    upload_file = request.POST["upload_file"]
    image_type = imghdr.what(upload_file.filename, upload_file.value)
    if not image_type:
        return "error"
    else:
        return image_type

>>> import Image
>>> im = Image.open("lena.ppm")
>>> print im.format, im.size, im.mode

import magic

ms = magic.open(magic.MAGIC_NONE)
ms.load()
type =  ms.file("/path/to/some/file")
print type

f = file("/path/to/some/file", "r")
buffer = f.read(4096)
f.close()

type = ms.buffer(buffer)
print type

ms.close()