It is possible to serve markdown files over gemini protocol (so says the specs: https://gemini.circumlunar.space/docs/specification.gmi). As for the tables, images, etc., it's up to a client (browser) to render it. For example, even though gemtext doesn't specify displaying images among text, some clients can display links to images as actual images inside the same page. Luckily, the gemtext is at least very similar to markdown, save for the link markup.