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.