Hah, so far so good! Here is my sample output and the original image (same as my profile pic here).
I can see it needs some work. The original image's aspect ratio is 16/9, but my ascii ouput is 1/1, so the image is being stretched vertically. Also, I'm only using 10 characters and the default font because typography is hard. I should go talk to the art department and find a student who likes working with fonts, to optimize selecting the right character for a block of pixels.
Still, it feels like a good first step.