Can a GPL project use proprietary resources (icons) as part of it? What I mean is that if it is possible that there is a repository covered by a GPL license that has a build script that downloads resources from another repo (and these resources are covered by non-OSS license - permission for private use without redistribution rights).
There would be an official distribution (build) of software using icons with permission for private use without redistribution license, but one could build their own fork or build of software, but would have to use their own image resources.
Is a concept like this compatible with GPLv3 or would this not work out?
The thing is that the software is rich with icons that I paid a designer to make and I would like to distribute the software in OSS means, but keep these icons in my ownership (and distribute my build with these icons only).
I know one needs to provide full build script and build instructions with GPLv3 software, so the question is if not offering icons would break this rule?