def normalize_extension(extension):
    """
    Normalize extension
    Converts given extension to canonical format for storage
    :param extension: original extension
    :return: normalized extension
    """
    extension = extension.lower()
    exts = dict()
    exts['jpg'] = ['jpeg', 'jpe', 'jif', 'jfif', 'jfijp2', 'j2k', 'jpx',
        'jpf', 'jpm']
    exts['tif'] = ['tiff']
    exts['tar.gz'] = ['tgz']
    for canonical, variants in exts.items():
        if extension in variants:
            extension = canonical
            break
    return extension
