Statutorily, in US law, as “a work on the copies or phonorecords of which no natural person is identified as author” (17 USC §101.) More practically, an anonymous work presents the problem that if authorship is unidentifiable the holder of rights in the work is unknown, and as a result no agreements to use the work can easily be entered into. If the work infringes an earlier work (i.e., it is a derivative work), it is hard to identify who claim of infringement should be made against. Anonymous works can also have hard to determine copyright terms, since the life of the author or artist is not readily determinable.