'Return the extension for the thumbnail image type as specified
by L{self.thumbnail_type}. If the LRF file was created by buggy
software, the extension maye be incorrect. See L{self.fix_thumbnail_type}.'

def thumbail_extension(self):

    ext = 'gif'
    ttype = self.thumbnail_type
    if (ttype == 17):
        ext = 'jpeg'
    elif (ttype == 18):
        ext = 'png'
    elif (ttype == 19):
        ext = 'bmp'
    return ext
