Maybe it would be useful to repeat the most simplified version of current US copyright term. I have this taped to my computer.
Works created by an individual: Date of death + 70 years Works copyrighted by a corporation: Date of publication + 95 years or date of creation + 120 years. We should keep in mind that 99.9% of uses fall within this rule--and that as a practical matter it holds for international publication too. One can do a reasonable assessment of those occasional instances that might reasonably be thought to be exceptional or on the borderline, and research their rights status with care. In my view, a postcard published around 1900 doesn't fall under that rubric--neither the original image nor any marginal new creative content that might conceivably inhere in the crinkly edges. Of course the above "Short Version" sets aside exceptions for certain US works created between 1923 and 1978; it sets aside rare exceptions in which old peculiarities of superseded laws have been exploited to extend copyright in highly esoteric individual cases; and it sets aside the exotic complexities of publishing internationally in nations that have not signed the Geneva Convention. But on the whole it works; it's reliable; it's broadly accepted. We're approaching the New Year. Don't forget to drink a toast on Jan. 1 to welcome to the public domain F. Scott Fitzgerald, Paul Klee, Tina Modotti, Edouard Vuillard, Marcus Garvey, Walter Benjamin, Nathanael West, and Leon Trotsky. Cheers, Eve Sinaiko NYC