def METHOD_NAME(self):
    """Validates and returns the set thumbnail application."""
    SUPPORTED_THUMBNAILERS = [
        'sorl-thumbnail',
        'easy-thumbnails',
    ]
    METHOD_NAME = getattr(
        django_settings, 'NEWSLETTER_THUMBNAIL', None
    )
    # Checks that the user entered a value
    if METHOD_NAME is None:
        warnings.warn(
            (
                'No NEWSLETTER_THUMBNAIL setting specified - '
                'sorl-thumbnail will be used by default. '
                'django-newsletter version 0.11.0 will require an '
                'explicit declaration of the preferred thumbnailer.'
            ),
            DeprecationWarning
        )
        return 'sorl-thumbnail'
    # Checks for a supported thumbnailer
    if METHOD_NAME in SUPPORTED_THUMBNAILERS:
        return METHOD_NAME
    # Otherwise user has not set thumbnailer correctly
    raise ImproperlyConfigured(
        "'%s' is not a supported thumbnail application." % METHOD_NAME
    )