@dansup support LLaVA or similar model for alt-text generation describing images.
The @IceCubesApp for Mastodon does this very well (see example image and auto generated alt text below) and may be worth a look. Also this article from @joe was useful for me in understanding where to start with this.
https://jws.news/2024/how-can-you-use-llava-and-node-js-to-describe-an-image/