Do derivative works of Creative Commons BY-NC works also have to be noncommercial?

Question

I've created an image that uses some source images that have been released under a Creative Commons Attribution-NonCommercial 3.0 US license. This license is not a share-alike license, meaning that derivative works do not need to be released under the same license.

I was wondering, however, if I could also release my derivative work to the public domain and use it commercially, or whether that would count as "using the BY-NC work commercially". I don't actually plan on doing so just yet, but I've never gotten a straight answer to this question since most people who include the non-commercial clause also have the share-alike or no-derivative-works clause in there as well.

It seems to me personally like it wouldn't count, just because the clause doesn't put any explicit restrictions on derivative works like the addition of a share-alike or no-derivative-works clause would and it doesn't seem in the spirit of Creative Commons to include implicit restrictions like a cascading non-commercial requirement. However, I'd like to make sure before I accidentally do something that unintentionally infringes the license.

Answer 1

_{I am not a lawyer. You should get one, if you are concerned about possible legal issues.}

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Of course, they have. You just cannot grant more rights than you have obtained, so there is no option for you to release a derivative work as a whole¹ to the public domain, or under any free/libre license, or in general any license, that is more permissive than CC-BY-NC. However, you could release it under more restrictive license, such as CC-BY-NC-ND for example. If the license of original work were copyleft one (i. e. *-SA), you could not do the latter – that’s the difference.

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¹ If it’s technically possible to represent your part of the work separately from original work, you may put it under CC0 or CC-BY, but the result, as long as it includes CC-BY-NC’ed part, still shall be covered by CC-BY-NC. It actually makes perfect sense if your part of work might be useful out of context of that non-free image.