The question is, why would Russian (or any other country's) copyright law have any effect on what you wanted to digitise or publish in the US?


Surely in the US you apply US copyright law, irrespective of the copyright status of the work in Russia or anywhere else. Only if you were trying to market a book or other product *into* Russia might you need to worry about Russian law. But to scan and host the digitised material  in the USA, it's US law that applies, whether the material is public domain in Russia or not.


Brendan Whyte