ALLOWED_EXTENSIONS = {'png', 'jpg', 'jpeg', 'gif'}


def allowed_file(filename):
    """ Ensures only filenames ending with the correct extension are allowed.
        Note: This does not verify that the content inside of the file
        matches the type specified
    """
    return '.' in filename and \
           filename.rsplit('.', 1)[1].lower() in ALLOWED_EXTENSIONS