Не удается идентифицировать файл изображения ImageFieldFile

Я использую django с Python, в моих models.py я объявил модель Tournament с изображением и атрибутом, это метод сохранения:

import datetime
from django.db import models
from django.utils import timezone
from tinymce.models import HTMLField
from rules.models import Rule
from news.models import Tag, News
from courts.models import Court
from news.models import replace_spaces
from datetime import datetime
from sorl.thumbnail import ImageField, get_thumbnail
from PIL import Image
from django.core.files.storage import default_storage as storage
from django.conf import settings

class Tournament(models.Model):
    name = models.CharField(max_length=50, default='', verbose_name='Nombre')
    name_url = models.CharField(max_length=200, default='', editable=False)
    inscription_opening_date = models.DateField('fecha de apertura de inscripcion')
    inscription_closing_date = models.DateField('fecha de cierre de inscripcion')
    tournament_starting_date = models.DateField('fecha de inicio del torneo')
    tournament_ending_date = models.DateField('fecha de finalizacion del torneo')
    description = HTMLField(default='', verbose_name='Descripcion del Torneo', blank=True)
    image = ImageField(upload_to='tournamentpic', verbose_name='Imagen')
    situation = models.ForeignKey(TournamentSituation, default='', verbose_name='Estado del Torneo')
    tournament_format = models.ForeignKey(TournamentFormat, default='', verbose_name='Formato del Torneo')
    regulation = models.ForeignKey(Rule, default='', verbose_name='Reglamento')
    tournament_type = models.ForeignKey(TournamentType, default='', verbose_name='Tipo de Torneo')
    tournament_category = models.ForeignKey(TournamentCategory, default='', verbose_name='Categoria de Torneo')
    quota = models.IntegerField(default=0, verbose_name='Cupos')
    tag = models.ManyToManyField(Tag)
    price = models.DecimalField(default=0, max_digits=6, decimal_places=2, blank=True)
    zones = models.IntegerField(default=0, verbose_name='Zonas', blank=True)
    KNOCKOUT_OPENING_CHOICES = (
        ('64', 'Ronda de 128'),
        ('32', 'Ronda de 64'),
        ('16', 'Ronda de 32'),
        ('8', 'Octavos de Final'),
        ('4', 'Cuartos de Final'),
        ('2', 'Semifinal'),
    )
    knockout_opening_round = models.CharField(max_length=2, verbose_name='Instancia de Inicio de Llaves', choices=KNOCKOUT_OPENING_CHOICES, default='32', blank=True)
    singles = models.IntegerField(default=0, verbose_name='Numero de Singles', blank=True)
    doubles = models.IntegerField(default=0, verbose_name='Numero de Doubles', blank=True)
    photo_full_size = models.CharField(max_length=255, blank=True, editable=False)



def save(self):
    self.name_url = replace_spaces(self.name)
    sizes = {'full': {'height': 415, 'width': 620},}

    extension = self.image.name.rsplit('.', 1)[1]  # the file extension
    now = datetime.now()
    date = now.strftime("%H-%M-%S-%d-%m-%Y")
    self.image.name = date +'.png'
    filename = date

    super(Tournament, self).save()
    default_format = 'PNG'
    im = Image.open(self.image)

    if extension not in ['jpg', 'jpeg', 'gif', 'png']: sys.exit()

    new_size = im.resize((sizes['full']['width'], sizes['full']['height']), Image.ANTIALIAS)
    medname = "-" + str(sizes['full']['width']) + "x" + str(sizes['full']['height']) + ".png"
    thumb_path = UPLOAD_TO + filename + medname
    fh = storage.open(thumb_path, "w")
    new_size.save(fh,default_format)
    fh.close()
    self.photo_full_size = thumb_path

Когда я сохраняю новый турнир в своей админке, я получаю следующую ошибку:

cannot identify image file <ImageFieldFile: 16-16-58-19-06-2015.png>

Я загружаю свои фотографии и медиафайлы на S3. Странно то, что в другой модели, с точно такой же конфигурацией работает отлично! Вот другая модель:

from django.db import models
from tinymce.models import HTMLField
from datetime import datetime
from sorl.thumbnail import ImageField, get_thumbnail
from PIL import Image
from django.core.files.storage import default_storage as storage
from django.conf import settings

import sys

MEDIA_URL = getattr(settings, 'MEDIA_URL')

UPLOAD_TO = 'aboutpic/'

class Name(models.Model):
    name = models.CharField(max_length=20, default='', verbose_name='Nombre')
    lastname = models.CharField(max_length=20, default='', verbose_name='Apellido')

    def __str__(self):            
        return self.name + ' ' + self.lastname

class About(models.Model):
    image = ImageField(upload_to='aboutpic', verbose_name='Imagen de Portada')
    introduction = HTMLField(default='', verbose_name='Cuerpo de Noticia', blank=True)
    creation_date = models.DateField('fecha de publicacion', default=datetime.now(), editable=False)
    names = models.ManyToManyField(Name)
    photo_full_size = models.CharField(max_length=255, blank=True, editable=False)

    def save(self):
        sizes = {'full': {'height': 415, 'width': 620},}

        extension = self.image.name.rsplit('.', 1)[1]  # the file extension
        now = datetime.now()
        date = now.strftime("%H-%M-%S-%d-%m-%Y")
        self.image.name = date +'.png'
        filename = date

        super(About, self).save()
        print self.image
        default_format = 'PNG'
        im = Image.open(self.image)
        if extension not in ['jpg', 'jpeg', 'gif', 'png']: sys.exit()

        new_size = im.resize((sizes['full']['width'], sizes['full']['height']), Image.ANTIALIAS)
        medname = "-" + str(sizes['full']['width']) + "x" + str(sizes['full']['height']) + ".png"
        thumb_path = UPLOAD_TO + filename + medname
        fh = storage.open(thumb_path, "w")
        new_size.save(fh,default_format)
        fh.close()
        self.photo_full_size = thumb_path

        super(About, self).save()

    def get_full_size(self):
        return MEDIA_URL + self.photo_full_size