tl;dr: Right now we are not allowed to quote outside sources (unless they are compatible with cc by-sa 4.0) or use images under fair use exceptions in our posts. Creative Commons provides guidance how to fix this, lets implement it.

According to the creative commons license when quoting text or images under a fair use exception we are supposed to exempt the text in question from the creative commons license.

The Creative Commons FAQ explicitedly describes best practises on how to do this:

For example, if your CC-licensed slide deck includes a Flickr image you are using pursuant to fair use, make sure to identify that image as not being subject to the CC license.

Source: Copyright by Creative Commons used under a Creative Commons Attribution 4.0 International license and exempt from the CC 3.0 license on this site

But the terms of service say

You agree that any and all content, including without limitation any and all text, graphics, logos, tools, photographs, images, illustrations, software or source code, audio and video, animations, and product feedback (collectively, "Content") that you provide to the public Network (collectively, "Subscriber Content"), is perpetually and irrevocably licensed to Stack Overflow on a worldwide, royalty-free, non-exclusive basis pursuant to Creative Commons licensing terms (CC-BY-SA)

Source: ©2019 Stack Exchange Inc terms of service and exempt from the CC 3.0 license on this site

In other words, if my understanding is correct the footer should include something like

Except otherwise noted user contributions licensed under cc by-sa 4.0 with attribution required

And then the ToS should include some type of exemption allowing users to exempt certain parts of their user contribution if they themselves are exempted under fair use/citation law.

And for all old content automatically under each blockquote include text exempting it from the CC license?

Also worth noting that all old content from before the CC 3.0 to CC 4.0 change should be exempted in the same way.

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    Related: Allow sourcing in blockquote markdown Commented Apr 30, 2019 at 10:34
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    If we look at European copyright law, which does not contain fair use, as it currently stands and also with the new directive that will go in effect, if it's not cc-by-sa 3.0 or compatible, you're technically not allowed to upload/use it here. Unless an image allows you to re-license it it's copyrighted and thus not allowed to be used here. But it doesn't stop there, some European countries also allow copyright claims on building photos, citing copyright to the architect, program designs/interfaces, so it's really tricky. I would advice to err on the side of caution. Commented Apr 30, 2019 at 14:08
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    @Tschallacka Citations however if my understanding isn't mistaken are allowed under EU law (although if I understand it correctly an author will be able to actively not allow citations, but it would be allowed by default). Anyway, citations seem to be a far bigger issue than images~ Even this question currently is breaking the law/ToS/CC license. Commented Apr 30, 2019 at 15:01
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    Citations are allowed, but be careful with citations, citations need to follow rules of attribution(author And work), and may only take up an insignificant portion of the encompassing work. Talking from an European perspective. Commented Apr 30, 2019 at 15:04
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    @Tschallacka great input, could your comments be provided as an answer?
    – ocæon
    Commented May 1, 2019 at 2:20
  • @ocæon done. Is a bit rambly and such, but I think I got the gist in it? Copyright law is complicated and a headache. Commented May 1, 2019 at 7:55
  • I think a clarification is in order regarding citations: while you are not allowed to quote outside sources (i.e. copy content from them), I highly doubt copyright law prevents you from citing them in the sense of identifying the source (e.g. giving its title, author, publication year, URL, etc.). I assume you're using the word "cite" with a different meaning than what I know it as, but other people may not know the distinction so I'd suggest clarifying that.
    – David Z
    Commented Apr 28, 2020 at 1:03
  • @DavidZ Fairly sure that 'quoting' is a type of 'citing', but you're right that the non-quoting type of citing is probably (actually now that I think about it not entirely sure) not an issue. Commented Apr 28, 2020 at 6:19
  • @DavidMulder My point is that in the usage I'm familiar with, "quoting" is not a type of "citing". I don't know how widespread this usage is but I'm assuming I'm not the only one who knows it that way.
    – David Z
    Commented Apr 28, 2020 at 6:40
  • @DavidZ Quoting is a right granted by the Berne Convention on Copyright. As to citing, I used to think there could be not legal opposition to it, but then some legislators got the idea of link taxes... Commented Apr 28, 2020 at 7:27
  • @DavidZ For whatever it's worth, they are listed as synonyms on vocabulary.com/dictionary/citation (including the explicit "a passage or expression that is quoted or cited"). I think it might be an "academia" vs "the rest of the world" thing, but not sure. Anyway, changed it straight away when I saw your comment. Commented Apr 28, 2020 at 11:02
  • @curiousdannii It indeed provides an exception, but that doesn't allow you to publish it under something like creative commons. Imagine a short story, and 100 reviewers quoting 100 different portions from that short story and publishing their reviews under a CC license. The end result would be that someone could take those 100 quotations and reconstruct a CC version of the entire short story. As that's not how it works CC explains in the linked resources that you should explicitly exempt such content from the CC license. Commented Apr 28, 2020 at 11:05

1 Answer 1


Talking from an European perspective, there is no fair use, and citation right is very limited, it needs to be a small part of the whole and properly attributed to source and author, and stand apart from the rest of the content as a citation(indentation, blockquote, other background, etc..)

But, the Stack Overflow ToS require everything to be licenced under CC-BY-SA license. A problem with the ToS is however that it does not specify which version of the CC-BY-SA license. It is implied by the one link in the ToS that it is CC-BY-SA 4.0 but it is not clarified which license applies to the content, since there are slight variations between all the versions between 1.0 and 4.0.
The confusion is further extended by the footer of the site which states CC-BY-SA 3.0. So conflicting messages are provided by Stack Overflow on which license to use.

Stack Overflow has clarified in their update that content posted before 2018-05-02 (UTC) is CC-BY-SA-3.0 and content on or after that date is CC-BY-SA-4.0.

For the sake of argument we settle on the CC-BY-SA 4.0 license because that is the one that is universally communicated by the footer of every site henceforth.
All content we share on Stack Overflow needs to be CC-BY-SA 4.0. So if some code is shared under another license that is not compatible you cannot use it.

You could for example use MIT expact license code in your question/answer and sub license it as CC-BY-SA when you also comply with the MIT conditions by adding the entire MIT license with it with the copyright header. That code now has TWO licences, the MIT license AND the CC-BY-SA license you added, and people can choose which license they want to use when they use the code, but Stack Overflow has their permission to use it because you sublicensed it to CC-BY-SA, so you comply with their ToS.

Images that don't have a CC-BY-SA compatible license, you cannot use them. End of story really. If the license conditions are not compatible, and there is not a right to sublicense, you cannot use them here.

Some countries have citation laws/precedents for images, like the Netherlands https://www.iusmentis.com/auteursrecht/citeren/beeldcitaat/
But you can't really count on it to be universially applicable, because like the Netherlands it used to be very confined in how things should be cited.

Not to talk about copyright about things within the images. https://www.diyphotography.net/10-famous-landmarks-youre-allowed-photograph-commercial-use/ so if you have a screenshot of your game/movie/programming editor you have to be careful. The contents of the game/movie are protected, the layout of the programming editor may be protected under copyright law, and if it's the main part of the question and not properly attributed per citation laws, it doesn't fall under it. And, as stated before, in Europe, there is no fair use. And the commercial use does apply because Stack Overflow is a commercial entity, even if you aren't.

Right now it's OUR problem, as contributors which license the content has we post, because we are liable for breaches, and Stack Overflow can simply say "Wasn't me".

But with the new Copyright reform in the European union that will go in effect in less than two years it becomes Stack Overflows problem too.
As the directive currently stands, Stack Overflow will have to delete reported content, as it does currently, but also build a feature that will prevent the same content from ever to be submitted again. (my personal opinion as I read that directive requirement was: A simple hash of the content suffices, and simply hash match. It only needs to be an exact match of that exact content, but it's waiting on the national implements of the law how strict it will roll out)

For those who say, but Stack Overflow is in the great USA and doesn't have to listen to Europe, yes that would apply if Stack Overflow would go black on all users outside of USA. The Berne convention has it so that anything that is performed in a country has to obey that countries copyright laws. So Stack Overflow has fair use in the USA, and publish a photo of the Eiffel tower at night in the USA, but to a user accessing Stack Overflow from France it can't.

It would be better if we could choose individual parts of licenses for separate parts of code and images, and the contributor is made responsible for maintaining the licenses and made aware of the license it's contributed under, without having to unilaterally share it under CC-BY-SA, but that would make things harder for datadumps, api's etc.. what Stack Overflow provides.

So in short: if it's not CC-BY-SA or permissibly sublicenseable as CC-BY-SA you cannot and may not use it here.

  • It only needs to be an exact match of that exact content, but it's waiting on the national implements of the law how strict it will roll out remains to be seen, as far as I know some countries in the EU plan to implement the copyright directive as requiring "state of the art" heuristic upload filters to pre-empt content that could be copyrighted from being uploaded, e.g. like a more aggressive version of youtube's content-id system.
    – Magisch
    Commented May 2, 2019 at 8:22
  • @Magisch Yea, but until those law texts are set in stone I only have the directive to guide, and that's awfully broad, and to comply with minimum effort you could do a hash match, and then take it to European court to knock down the heuristics requirement if you have breath and finances that long when the country laws are provided. The European courts have been good at knocking down ridiculous requirement or overly broad laws. And the directive doesn't require to pre-emt, only after the fact that it was uploaded and reported forbids re-uploading. pre-empt would be a national thing only. Commented May 2, 2019 at 8:30
  • I would think clearly stating in the post that the code cannot be licensed as CC should be enough to not license it as CC as the intent is clearly stated. But SO may choose to remove it completely, when they do not want non-CC code on their site. Just think of someone posting a snippet of GPL code from a project he is part of. He cannot sublicense it, so SO cannot even get a CC licensed version of it. The only thing SO can do is to remove the code or the whole post (to remove the code in the edit history of the post as well).
    – allo
    Commented Mar 2, 2020 at 13:17
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    @allo You cannot, an may not upload code that is not compatible with CC-BY-SA as sharing or dual licensed if you are not authorized to do so. So unless you are the author of said code, you are not in the power to re license the code under an incompatible license. No matter what you say in the post. You agreed to the terms of service where you agree to share under CC-BY-SA. You are the one on the hook for violation of the license provided to you. The only way to include it is to use it as a citation, and that can get murky as well Commented Mar 2, 2020 at 13:34
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    "Fair use" may be a term specific to the US, but note that the Right to Quote is part of the Berne Convention on Copyright. Though whether that applies to images as well as text is murky. Commented Apr 28, 2020 at 7:22

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