def METHOD_NAME(mbid, coverid, size=None, entitytype="release"):
    """Download cover art for a release. The coverart file to download
    is specified by the `coverid` argument.
    If `size` is not specified, download the largest copy present, which can be
    very large.
    If an error occurs then a :class:`~musicbrainzngs.ResponseError`
    will be raised with one of the following HTTP codes:
    * 400: `Releaseid` is not a valid UUID or `coverid` is invalid
    * 404: No release exists with an MBID of `releaseid`
    * 503: Ratelimit exceeded
    :param coverid: ``front``, ``back`` or a number from the listing obtained with
                    :meth:`get_image_list`
    :type coverid: int or str
    :param size: "250", "500", "1200" or None. If it is None, the largest
                 available picture will be downloaded. If the image originally
                 uploaded to the Cover Art Archive was smaller than the
                 requested size, only the original image will be returned.
    :type size: str or None
    :param entitytype: The type of entity for which to download the cover art.
                       This is either ``release`` or ``release-group``.
    :type entitytype: str
    :return: The binary image data
    :type: str
    """
    if isinstance(coverid, int):
        coverid = "%d" % (coverid, )
    if isinstance(size, int):
        size = "%d" % (size, )
    return _caa_request(mbid, coverid, size=size, entitytype=entitytype)