Any ethical claim to ownership over a scan of a public domain work should be treated with utmost suspicion, not least because of all the people with stronger claims than the scanner! To be consistent with the ethical principle that one should never use another's work without permission (regardless of the law or the public domain), every scanner would have a duty to ask, at the very least, the corporations whose products are advertised in these old chestnuts (the very best of them are for brands that persist to today, since these vividly illustrate the way that our world has changed - for example, see the very frank Lysol douche ad). For if scanning a work confers an ownership interest, then surely paying for the ad's production offers an even more compelling claim!Proprietary Interest
And the publishers of the magazines and the newspapers - to scan is one thing, but what about the firm that paid to physically print the edition that we make the scan from? And then there are the copywriters and illustrators and their heirs - if scanning an ad confers a proprietary interest, then surely creating the ad should give rise to an even greater claim?
We do acknowledge these claims, at least a little. A good archivist notes the source. A good critic notes the creator. But that is the extent of the claim's legitimacy. If we afford descendants and publishers and printers and commissioners their own little pocket of customary right-of-refusal over their works, we would eliminate the ability to keep these works alive in our culture. For these owed courtesies multiply geometrically - think of the challenge of getting all of Dickens' or Twains' far-flung heirs to grant permission to do anything with their ancestors' works. What a lopsided world it would be if ten seconds' scanner work with the public domain demanded 100 hours' correspondence and permission-begging to be ''polite!''