what do we think about massively spoilering it to upload here? Not just a subtle watermark, but in such a way that the essence of the question is preserved, but any possible re-use of the image is totally destroyed?
IMO, this is not necessary, and perhaps even not advisable. Why should people other than the asker go through the work to scale down, "bowdlerize", or otherwise create a derivative work to upload? We shouldn't.
The simple thing is to ask the asker to edit their question to upload the image into the question. It's not up to us, or even Stack Exchange, to take it upon ourselves to try to enforce somebody's copyright, or attempt to make our own interpretation of what is acceptable "transformation" of 3rd party work. We're not lawyers.
Personally, I would be okay with closing such questions if they don't explicitly upload the image to their question AND cite attribution in the question text. Yes, that would be asking the OQ to upload a 3rd party image, probably without their consent. But it's not clear if the consent is needed (i.e., does it constitute fair use), and regardless, Stack Exchange responds to all DMCA takedown requests per their policy.
Citing Shog9's answer to: I'm tired of whining about copyright violations. Can we get an official solution?:
The not my job game
Now, back to the "it's not your job to enforce this" bit...
It's not your job to enforce anyone else's copyright. And in most cases, you probably shouldn't try...
...But that's not to say we can't establish and enforce some policies here on Photography.SE that serve to discourage copyright violation, encourage quality content, and stand as clear, easy-to-interpret guidelines for both authors and reviewers.
- All images posted here must be either owned by the person posting them, or have their source clearly cited in the surrounding text.
- A post consisting solely of an image or images not owned by the author or authors of the post must be removed.
- Images containing photographic or artistic renditions of the duck-billed platypus will result in immediate suspension.
In other words, it's your site - if you collectively decide to collectively enforce a set of rules governing the content posted here, that's your prerogative - you don't need (or particularly want) to lean on something as hairy as copyright law for your standards of quality - there are plenty of better reasons (ethical and practical) for excluding misrepresented, plagiarized or lazy content.
Related, Should we disallow hot-linking?. I'm not advocating disallowing hot-linking, but referring back to Shog9's answer above, in the case of "how do I achieve this effect?" questions, we can absolutely make that rule if we want to.