fields.py

from django.db.models import FileField
from django.forms import forms
from django.template.defaultfilters import filesizeformat
from django.utils.translation import ugettext_lazy as _


class ImageFieldRestrict(FileField):

    def __init__(self, *args, **kwargs):
        self.content_types = ['image/jpeg', 'image/gif']
        self.max_upload_size = 2242880
        super(ImageFieldRestrict, self).__init__(*args, **kwargs)

    def clean(self, *args, **kwargs):
        data = super(ImageFieldRestrict, self).clean(*args, **kwargs)
        file = data.file
        try:
            content_type = file.content_type
            if content_type in self.content_types:
                if file._size > self.max_upload_size:
                    message = 'Please keep filesize under {}. Current file size %s'
                    message = message.format(filesizeformat(self.max_upload_size), filesizeformat(file._size))
                    raise forms.ValidationError(_(message))
            else:
                raise forms.ValidationError(_('Filetype not supported.'))
        except AttributeError:
            pass

        return data

models.py

from .fields import ImageFieldRestrict

class Photo(models.Model):
    user = models.ForeignKey('auth.User', related_name="user_photos")
    booklet = models.ForeignKey(Booklet, related_name="photos")
    about = models.CharField(max_length=100)
    pic = ImageFieldRestrict(upload_to='photo/%Y/%m/%d')
    created = models.DateTimeField(auto_now_add=True)

    def __str__(self):
        return self.booklet.title

    class Meta:
        ordering = ('-created',)