The  Digital Millennium Copyright Act does address unpublished material and provides additional protections over the 1978 revisions as follows under sections 302 and 303:

120 years from the creation of the work - pre-1882 unpublished material will no longer protected after December 31, 2002. New material will be effected each year, unpublished material from 1883 will loose protection December 31, 2003, etc.

Works created but not published or copyrighted before January 1, 1978 that are subsequently published before December 31, 2002 are protected until at least December 31, 2047 or until the earliest of the following conditions are met:

 -70 years after the death of the author or longest surviving author for joint works.

 -95 years after publication for anonymous works or works made for hire.

The definition of publication and it's impact on photographs is somewhat open to interpretation. Are works for hire considered published if presented internally to the hiring agency, or only if presented to the general public? Are they anonymous if uncredited in the publication though known to the agency, etc. Also there are a number of efforts to clarify and challenge several elements of the DMCA that may have some impact on the definitions and there is continual additional movement as the U.S. attempts to comply with international treaties and copyright agreements.