Get a set of objects from different models field names

[Aamu Padi]

Please have a look at my models.

    class BackgroundImage(models.Model):
        user = models.ForeignKey(User)
        image = models.ImageField(upload_to=get_upload_file_name)
        caption = models.CharField(max_length=200)
        pub_date = models.DateTimeField(default=datetime.now)

    class ProfilePicture(models.Model):
        user = models.ForeignKey(User)
        image = models.ImageField(upload_to=get_upload_file_name)
        caption = models.CharField(max_length=200)
        pub_date = models.DateTimeField(default=datetime.now)

    class Album(models.Model):
        user = models.ForeignKey(User)
        name = models.CharField(max_length=200)
        pub_date = models.DateTimeField(default=datetime.now)

        class Meta:
            ordering = ['-pub_date']
            verbose_name_plural = ('Albums')

        def __unicode__(self):
            return self.name

    class Photo(models.Model):
        user = models.ForeignKey(User)
         album = models.ForeignKey(Album, default=3)
        image = models.ImageField(upload_to=get_upload_file_name)
        caption = models.CharField(max_length=200)
        pub_date = models.DateTimeField(default=datetime.now)

How do I get all the images of Photo, ProfilePicture and BackgroundImage from their image field in one set. And then filter them by -pub_date to display in the template? Please help me out. Will be much much appreciated! Thank you.