RE: CounterMeasures for Curators to Minimize Farming and Fraud
It might be a matter of respect to list sources that are in the public domain, but this is not required by law. It is patently silly to act holier than the Pope.
Conversely, if you use copyright images, listing the source does not get you off the hook for illegally using a image.
Imagine a collage artist who used hundreds of details from public domain images: do you expect a list of sources? For example, would you flag Max Ernst?
https://www.wikiart.org/en/max-ernst/collage
The other problem you might run into (and had done yourself at times with Jaguar photos) is if the "source" quoted is itself a stolen image. Like, if you get your image from a social site, or a website that posts unsourced images (such as for wallpapers). Also, some stuff on DeviantArt is ripped off, which is a ongoing concern, so if you cite a DeviantArt image as a source, how sure can you be that it is not already stolen?
Too bad you mentioned an artist who died in 1976 and you know better than me that there were no copyright rules, because the internet was far away.
For the rest, @jagur.force answer is exhaustive.
Citing the sources, for the correctness of any work with images is an ethical duty.
" that there were no copyright rules, because the internet was far away."
you should only comment about a subject you have at least a basic understanding of.
I researched and compiled extensive resources concerning copyright.
What I am talking about is that sources get nitpicked, while there are all kinds of copyright violations going on, even by the author of this post.
It is not only a matter of respect to list the sources, the reason why sources need to be credited is so the curators know what part of the composition/motive you created yourself and also so the curators can see to what level (if any) you transformed it. It is not a matter of law in that sense but of transparency and honesty, and as to allow viewers and curators to know what part (if any) you created yourself.
Certain CC licences (which is public domain) explicitly require attribution, so in those cases it is public domain and legally required to list the sources.
If you use a copyrighted image as reference, listing the source does not cover you legally as you say, but at least you are not deceiving curators and viewers into thinking the artwork is 100% created by you.
Using multiple sources doesn't except you from having to list the sources, curators and viewers still have the right to know what you created yourself and what comes from another author.
It is irrelevant from the perspective of curators and viewers if the source listed is not the original source, what is important within that context is that you communicate it's not created by you, but somebody else, who specifically is that somebody else is secondary.
Have a great day.
"Certain CC licences (which is public domain) explicitly require attribution, so in those cases it is public domain and legally required to list the sources."
.... as do mine (attribution, no derivatives, non commercial), and quoting the source is OK as long as you do not use it for commercial purposes, meaning since you are posting here for earning Steem, you are commercial, so quoting the source, as in any other copyright material, is not enough be be legal.
On the other hand, if you purchase the rights for an image it is yours to do with as you like (within the parameter of the license you bought).
so certain CC licenses require, legally, attribution, namely: you were wrong.
we do not post in any artistic tag, where the main content rewarded is artistic, although I agree with you hunting abusers can be called an art.
Have a great day.