According to this article that was just released yesterday, the unrestricted model of GPT-4 can produce images.

https://arxiv.org/abs/2303.12712

On page 16, "the model appears to have a genuine ability for visual tasks, rather than just copying code from similar examples in the training data. The evidence below strongly supports this claim, and demonstrates that the model can handle visual concepts, despite its text-only training"

I'm still not sure whether my initial assumption was from information I gleaned somewhere or because I hallucinated it. Regardless, GPT-4 can indeed output images.