After three months of torturous waiting, I finally got a response back from the poster publisher that had requested my images for review. I'm sure their response is obvious from the title of this post. They did say that my submission showed a great deal of talent and that I shouldn't interpret the letter as rejection but as an encouragement to submit new work in the future.
Still kind of feels like a rejection. At least the waiting is over.
However, it's been my experience that a rejection with an invitation to submit more work in the future is the most positive kind of rejection you can get-- and they're not lying to be nice (why would they? it's a waste of their time to look at your work if they don't like it). So keep sending them your work!
(I love this image, by the way.)