I'm a small-time open-access publisher, not a lawyer, but have done lots of research about this, and spoken to Creative Commons counsel about it. So I will make a proposal.
@Neo wrote in the question I mentioned:
i dont think that is a copy right issue: journals are meant to be
cited, as long as they are cited. I do not need any permission to use
a diagram from a journal article in any form, if properly cited.
At least in some jurisdictions, we can make a fair use argument. This is a matter of judgment and I agree that SE probably qualifies in most cases, provided the excerpts are small and properly cited and labeled (see below).
There is also the issue of Stack Exchange's open license, CC-BY-SA, which can in principle contain unlicensed material but probably shouldn't. Wikipedia, which uses the same license, has zero tolerance for it. There are exceptions, like a fair use claim for using a low-res cover image as a visual representation of a book, but even these are challenged all the time.
If a person really has to use unlicensed material, they should do three things:
- Ensure that the use complies with the rights holder's terms.
- Cite the source with a full bibliographic citation and, preferably, a DOI.
Notwithstanding all this, here's why I think we should strongly discourage the use of unlicensed copyrighted material:
- It would encourage the creation of more open access material, for example to illustrate a point.
- It would increase the impact of open work, like Wikimedia Commons, Figshare, PLOS ONE, and so on.
- It would reduce the impact of non-open work.
I realize this probably all seems pedantic to most people, but I think most of us would agree that open access to scientific knowledge is important for society, and copyright abuse is rife in our field (just go to a conference and watch the parade of unlicensed material in people's talks). Instead of ignoring the issue, we can play a part in growing the amount of open material in geoscience.