I spoke to the blog owner and provided proof that it was my work. The blog had posted the work in question with my permission a year prior, and it also had my signature at the bottom (which didn't match the submitter's name), so it was a quick process getting it removed. After speaking to the individual who submitted my work, they apologized and said they had found it on Twitter.
I'm still keeping track of this situation, but I have one question. What would be the best way to confront this situation? Should I let it go? Should I pursue it? Part of me says I should let it go, because it's not as if someone is profiting off it. But the other part of me is saying I should pursue this, because it's my work floating around the internet currently uncredited, and I would like to find the source which started this.
I've never had one of my pieces outright "stolen" like this before, and it's a confusing situation! Any and all advice would be appreciated.