For post #1579876, the source URL is http://i1.pixiv.net/img21/img/apple228/40504178_big_p0.jpg, abbreviated down to "pixiv/apple228". However, with, say, post #1994054, which has a source URL of http://i1.pixiv.net/img-original/img/2015/04/25/22/06/11/50022068_p0.jpg, it is shown as "pixiv.net/member_...".
Perhaps it would be better if it was shown as "pixiv #########" since you can't get the artist name directly from the latter URL?