Return image format for file-object f. (jpeg, png, gif etc.)
    All formats: http://pillow.readthedocs.org/en/latest/handbook/image-file-formats.html
    Example:
        if image_get_format(request.FILES['image']) == 'jpeg':
            print 'Image is JPEG'

        if image_get_format(open('/tmp/image.png', 'rb')) == 'png':
            print 'File is PNG'

def image_get_format(f):
    """
    Return image format for file-object f. (jpeg, png, gif etc.)
    All formats: http://pillow.readthedocs.org/en/latest/handbook/image-file-formats.html
    Example:
        if image_get_format(request.FILES['image']) == 'jpeg':
            print 'Image is JPEG'

        if image_get_format(open('/tmp/image.png', 'rb')) == 'png':
            print 'File is PNG'
    """
    f.seek(0)
    try:
        img = Image.open(f)
        t = img.format.lower()
    except IOError:
        t = None
    return t