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Let's say I'd like to develop an end-user application with which you can create some kind of artistic work (say presentations or drawings). As a fan of the open source idea, I'd like to open-source the full program's source code under a copyleft license (thus, requiring derivative works to be distributed under the same free license as well).

For end-users and educational institutions, this will be enough. However, for professional works (made by companies), I'd like to take a fair price for that same piece of software.

Now, the Dual Licensing concept is based on the idea that it will be impractical for commercial companies to distibute derivative works of the software, as it would have to be open-sourced as well.

For this artistic software though, I'm not particularly worrying about companies modifying and re-selling the software, but instead that the resulting works would be created with the copyleft-version instead of the commercial version.

Of course it would be easy to just restrict the copyleft version's functions and put like some disturbing watermark on the user's creations. But I don't want to go this cheap way. Is there any licensing model out there that covers this issue?

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Your idea is not going to work.

License terms for a copyrighted work can only be set/dictated by someone who has a copyright claim on the work. And just as Microsoft doesn't have a copyright claim on the documents you write with MS Word, in the same way you don't have a copyright claim on the artistic works created with your software.

For copyright purposes, a work and the software used to create it are completely independent of each other. The only exception to this is if the software includes a copyrightable portion of itself in the work you create with it. In that case, the resulting output most likely is a derivative work of the software, giving you a copyright claim on (parts of) it.

Now you might think about padding the output with portions of the program just to get a copyright claim, but that will in practice also not work effectively. As your software is open source, others have the right to remove the code that pads the output (or the code that adds the conspicuous watermark) and distribute the modified version.

If you want to monetize your open-source software, it is better to think in terms of selling support contracts rather than selling copies of the software.

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  • Thanks for this detailed answer. I see that my idea is practically not possible. Support contracts seem the way to go then, thank you! – fameman Jul 18 at 17:27
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    @fameman if you're happy with this answer, may I encourage you to accept it? If not, clarification of what it left unanswered will help with filling in the gaps. – MadHatter Jul 19 at 12:15

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