I think the English term "copyright" is somewhat inadequate to describe the whole matter, as it suggests that it's only about copying. Copyright means - if taken to the extreme - that the author CAN dictate how, when, where, by whom etc her/his 'product' may be used (from "not at all" to "ultimate freedom of use by anybody"). Nevertheless, any restriction set by the author expires the minute the copyright expires.

Whether the 'product' has been published or not, is of NO significance. If it can be 'evidenced' that the 'product' is by the author and s/he has been proved dead for more than 70 (well, 71 to be dead sure) years, the product IS public domain.

Thus, if I manage to smuggle a camera into "a museum of medieval art" (where no camera's allowed) and take photos of their complete collection (without the staff noticing, of course, and later turn them into a million seller book;-), they might sue me for who knows what, but NOT for breaking painters' copyrights.

AKS