Let's say it's 1910 and a photographer takes a photo but never publishes the original. Later someone else (with permission) uses that original photo to make a colorized postcard and publishes it. If the post card was published in, say, 1911, then it is public domain in the US, correct? But what about the original photo? Since the colorized version was published, is the original black-and-white version considered published as well? Or does it remain unpublished and therefore copyrighted for the usual creator's-lifetime-plus-70-years?
As you can see in this well-known chart, unpublished works have a US copyright term of 70 years after the author's death. Thus the original would be in the public domain if the author (photographer) died before 1949, but still under copyright if the death date is 1949 or later. If the date of the author's death is not known, copyright lasts for 120 years from the work's creation, so thru 2030 for a work created in 1910.
The 120-year term also applies if the author was anonymous, or used a pseudonym, and his or her actual name is unknown.
As DaleM said in the other answer, the derivative work has a separate copy right, and as that answer implied, publication of the derivative work does not constitute publication of the original. The original may or may not be in the Public Domain, depending on the date of the author's death.
This answer give copyright terms for united-states law. Terms in other countries are different.
Derivative works are separate works with distinct copyright terms
For your example, the derivative is public domain, the original is under copyright until 70 years after the photographer's death.