It was mentioned earlier in this thread that a copyright claim on a public domain image is based on originality and not sweat equity in the work.
So, in the case of someone who scans a public domain image and places it on their website, they may not have a legal leg to stand on, but I would argue that they may have an ethical one.
First of all, the only reason one has access to a particular public domain image is because someone took the time to scan it in and make it available. Is that not significant, especially considering that old books and magazines are frequently tossed without a care for the value of their contents? While that someone may not have a legitimate copyright claim in the work, certainly there is some ethical obligation to credit that someone as the source for your copy of the work, more so than the scanner engineers. The scanner engineers made a tool; the person operating the scanner decided how to put it to use.
Second, how does one know how much work someone put into the scan? If you don't have access to the original copy of the public domain image, how do you know how much work did or didn't go into it? Maybe the person operating the scan pressed "scan" and left it at that. Maybe they did some Photoshop work to restore it. In the former case, refer to point #1.
In the case of the latter, that being that some amount of sweat equity went into restoring the public domain image, while that may not give the person a legitimate copyright claim to the work, certainly there is an ethical obligation to credit the person who did the work. Restoration is not always an easy task. Photoshop (and other software) are great tools, but there is no "restore" button that will automatically take a public domain work and restore it to its original condition. Maybe when we have computers like on Star Trek that can be done, but today it takes the skill and hard work of a human being.
While that may not constitute a basis for a copyright claim, certainly it constitutes a basis for an ethical obligation to the person who did that work, no?
[edited by: ccDan at 2:36 pm (utc) on June 15, 2007]