Re: Unsplash, the DFSG, and the GPL

Soren Stoutner <[email protected]> Fri, 14 Mar 2025 12:10:45 -0700
Newsgroups	gmane.linux.debian.devel.legal
Organization	Debian
Message-ID	<2247153.hkbZ0PkbqX@soren-desktop>
On Thursday, March 13, 2025 10:33:25 PM Mountain Standard Time ziproot wrote:
> Hello all,
> 
> I am ziproot, a contributor to the video game Endless Sky, which has been on
> Debian repos in the past. I have a few questions concerning copyright.
> 
> 1. Endless Sky’s source code is licensed under the GNU General Public License
> v3 or later, however, there are images licensed under CC-BY-SA 3.0, CC-BY-SA
> 4.0, and the Unsplash License. Is this a violation of the GPL?

The CC-BY-SA 4.0 is not a problem for the GPL-3, but it isn’t compatible with the GPL-3+.

https://www.gnu.org/licenses/license-list.html#ccbysa

The CC-BY-SA 3.0 is not compatible with the GPL.

https://creativecommons.org/share-your-work/licensing-considerations/compatible-licenses/

The Unsplash License is not DFSG-free, and is not compatible with the GPL.  This is due to 
the last line in the license.

"This license does not include the right to compile images from Unsplash to replicate a 
similar or competing service."

> a. There are some binaries, such as an AppImage, which are packaged with the
> compiled source code and all of the images. Would this violate the GPL, or is
> this considered an aggregate? If this does violate the GPL, what would be
> necessary to make it GPL compliant? In other words, what images would need to
> be removed, or if possible, what would be necessary to include both the assets
> and the source code as licensed?

As Sebastian explained in a separate email, this isn’t a problem for the GPL as long as the 
source code is available that is used to create the binaries.  For Debian, if the binaries need 
to be a part of the Debian package, they should be compiled at build-time from the source 
code.

> 2. Are these licenses allowed in Debian repos? If not, which ones are not, and
> would it be possible to include Endless Sky in the contrib and/or non-free
> repos instead?
> 
> If you are unfamiliar with the Unsplash License, its terms are here: https://
> unsplash.com/license/

All of the licenses except Unsplash are DFSG-free, so they are allowed in the main 
repository (note that individual packages must use compatible licenses as described 
above).

Unsplash is not DFSG-free, so if you wanted to ship a package using it, it would have to 
ship in non-free.  (As an explanation, everything in main is DFSG-free.  Things in non-free 
are not DFSG-free in some way, but do grant distribution permissions.  Things in contrib 
are DFSG-free but depend on a package in non-free.)

However, as you can’t combine Unsplash or CC-BY-SA 3.0 code with the GPL, there is no 
way you can ship Endless Sky in its current state in Debian or anywhere else.

> If you wish to view the game's repository for more information, you can do so
> here: https://github.com/endless-sky/endless-sky/
> 
> Thank you for your support.

I hope this is helpful.  I wish you luck sorting out the licensing problems upstream.  My 
personal experience is that many upstream projects are not very careful about combining 
licenses that aren’t actually compatible.  Often, it is when a Debian package is being 
prepared that they are alerted to the fact that they have been shipping incompatible code 
for years.  Sometimes this is easy to fix upstream and sometimes it takes a lot of work to 
excise the incompatible licenses.

-- 
Soren Stoutner
[email protected]
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