ASCII or similar fallback

Right now this supports fallback text as discussed in #1. It might be worth considering an optional fallback that isn't as... sad.

[Here's an example](https://github.com/IonicaBizau/image-to-ascii) of a JS module that converts images to ASCII so you can display color images in the terminal in some capacity.

Trace the repository’s existing fallback text behavior, then review the linked image-to-ascii example for possible terminal output approaches. Clarify the optional fallback’s expected behavior and verify it with image cases; done means color images have a less limited fallback while the current default remains supported.

Written by the indexing model from the issue text.