Actually, it seems like a good question to me. The MIT license (and the other major ones, afaik) specifically applies to the software (and docs), not what artifacts the software might produce. It's not clear to me whether those would be included under the same terms. I would assume they're free to use, but I'm not sure that's (always) true and IANAL.

Something to think about: if I write a program that outputs a work under copyright (without actually containing the copywritten work), can I still use a permissive license?