Back in February, the Creative Commons organization began taking steps to introduce compatibility between their licenses and the GPL. At that time, we took notice and started discussing the problems we’ve had with CC licenses in the directory in the past.
Part of the problem is that the Creative Commons licenses are so fragmented. It’s very much a choose-your-own adventure landscape for CC licenses, and many people don’t understand licensing very well in the first place (it can be confusing, I admit).
Since we require everything in our directory to be GPL Compatible, then it’s something we have to constantly scan for when even an accidental violation occurs.
Then, things became even more interesting in March, when gnu.org silently changed their compatibility page to state that CC-BY 4.0 was now considered compatible with all versions of the GPL. So, at that time, we started trying to ignore that particular case. It isn’t easy, because a lot of CC licensed code is licensed under version 3.0 of their licenses, which is not GPL Compatible. And the issue of CC-BY-SA was still very much up in the air.
However, last month, Creative Commons finally stepped up. CC-BY-SA 4.0 is now compatible with the GPLv3.
Accordingly, you can now use CC-BY 4.0 and CC-BY-SA 4.0 licensed code or images or anything else in the WordPress.org plugin and theme directories.
A few points of note:
- Only version 4.0 is acceptable. Check before using third party code which may still be licensed using 3.0.
- Only the Attribution (BY) and Share-Alike (SA) clauses are acceptable. The No-Derivs (ND) and Non-Commercial (NC) clauses are definitely not GPL-Compatible. Code or images using them cannot be used.
- If the code you’re wanting to use has the Share-Alike (SA) clause, then it is only compatible with the GPLv3, not GPLv2. This means your plugin and all the other code in it must be licensed under the GPLv3. The GPLv2 is not compatible with the GPLv3.
If you need it in simpler terms:
- CC0 – This is equivalent to a public domain declaration, essentially, compatible with everything, and we have always allowed it.
- CC-BY 4.0 – Compatible with any version of the GPL.
- CC-BY-SA 4.0 – Compatible with the GPLv3 only.
- Previous versions of CC licenses (like 3.0) – not compatible.
- Any CC license containing “NC” or “ND” terms – not compatible.
So, if you have a favorite library or image that we’ve had to push back on you in the past for, take another look at it. The license might be compatible now. Also, if something is CC 3.0, consider asking the author of the work to bump that up to 4.0, so you can use it. It’s nicer for everybody to have more things out there compatible with each other.
(Note: everything above applies to themes too. I just don’t want to write two posts. )