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So I had been using trianglify, and I was thinking about using an image that it had created. Trianglify is licensed under GPLv3, however, (as I understand it,) it creates unique svg files. The author has not included any instructions as to how to source/license these images, so I was thinking about sourcing the image in my GitHub .readme file for my project.

My question is, would I have to also change the licensing of my code to be under the GPLv3 if I am only using an image derived from the licensed product? What should I do? I'm not using any of the code, just its (unique) product (an image). Or would this be on a case by case basis where I would have to contact the author (if so, for each usage or just once)?

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The GPL describes rules about the use of the source code, not rules about the use of products of the application itself. The most obvious example is the GNU compiler. The compiler is released under the GPL. It is perfectly fine to use that to compile programs that are not released under the GPL. What you are restricted from is modifying the GNU compiler itself and not putting those modifications under the GPL. Lots of very proprietary code is compiled with the GNU compiler.

This is generally true of most open source licenses, however, I suppose it might not be the case for every single one. If you run into some weird license, read the license and perhaps consult a lawyer. But for the GPL and trianglify, you would not be restricted from using generated svg files in any way.

That said, pointing to the code that generated the file in your own .readme is a nice thing to do, and has no real downsides, so you might as well do it. But you aren't required to.

  • I've seen libraries and tools that in their licenses/TOS included restrictions on the licensing/rights of the created data/content. Don't ask me the legality of such things, but some programmers do try. – jwenting Apr 5 '15 at 4:45
  • Yeah, that's why I added the caveat about weird licenses. The most common licenses out there don't do that. – Gort the Robot Apr 5 '15 at 5:25
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    If such a license DID exist, wouldn't this be equivalent to putting an end user license on a tool like a saw and saying "all your woodworks are belong to us". IANAL as well but this sounds pretty ridiculous. BTW I produce plenty of content in proprietary products like MS Word, Visual Studio et al, and pretty sure none of that that I produce "belongs" to MS. – Brandin Apr 5 '15 at 10:29
  • I have an example of a licensing agreement that included such a limitation, actually. The Visual Studio Express IDEs, available for free from Microsoft, were for personal use only. You were not allowed to redistribute any application compiled by those IDEs. You had to purchase an actual copy of Visual Studio in order to sell/distribute the apps created by it. The latest incarnations of Visual Studio do not have this requirement anymore (that I could find), but that EULA was probably around for a decade or more. – phyrfox Apr 5 '15 at 11:06
  • This is pretty common, actually. It is a form of price discrimination and sometimes quality control. Microsoft generally forbids releasing software created using pre-release versions of MS products, for example. They also often forbid creating commercial products with their free offerings, e.g. for students. IntelliJ offers special licenses for IDEA, which can only be used to create open source software. For free/open software, however, this simply cannot exist, because both the Free Software Definition and the Open Source Definition forbid such field of use restrictions. – Jörg W Mittag Apr 5 '15 at 12:14
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Author here. Trianglify images are yours to do whatever you want with. You could even trademark a trianglify image to use in a logo. It's just a tool, what you produce using the tool is content that you own.

  • +1 for as authoritative an answer as one could hope for :-) – Ross Patterson Apr 10 '15 at 2:38
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No a piece of work created by a GPL piece of software is not generally a derived work.

There are exeptions, where for example, the GPL app is a code generator which produces source code containing significant bits of the original app. But producing an image, or any other piece of creative work with a GPL tool is not itself GPL.

  • Although it is worth noting that Bison, one of the most common code generating GPL programs, specifically makes its generated code not subject to the GPL. – Philip Kendall Apr 5 '15 at 5:51
  • According the the GPL FAQ Bison does this because it copies code to the output, which would otherwise be GPL. So it's a special case they've allowed for. – Gort the Robot Apr 5 '15 at 6:52
  • @PhilipKendall Bison's generated code is not GPLed, however its included code is GPLed. Bison is the canonical example of a program that generates GPLed output. – Ross Patterson Apr 10 '15 at 2:34
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This case is explained in the GNU GPL FAQ:

Is there some way that I can GPL the output people get from use of my program? For example, if my program is used to develop hardware designs, can I require that these designs must be free?

In general this is legally impossible; copyright law does not give you any say in the use of the output people make from their data using your program. If the user uses your program to enter or convert his own data, the copyright on the output belongs to him, not you. More generally, when a program translates its input into some other form, the copyright status of the output inherits that of the input it was generated from.

So the only way you have a say in the use of the output is if substantial parts of the output are copied (more or less) from text in your program. For instance, part of the output of Bison (see above) would be covered by the GNU GPL, if we had not made an exception in this specific case.

You could artificially make a program copy certain text into its output even if there is no technical reason to do so. But if that copied text serves no practical purpose, the user could simply delete that text from the output and use only the rest. Then he would not have to obey the conditions on redistribution of the copied text.

In what cases is the output of a GPL program covered by the GPL too?

Only when the program copies part of itself into the output.

So no, the output of a GNU GPL program is not covered by the GNU GPL and you can put it under any license conditions you want.

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