I like a significant amount of sites I can find through https://marginalia-search.com/explore

I don't think most of the ones I like would be possible to implement in gemini because it doesn't have images.

Gemini has images, just by default the gemini protocol is designed to not download and inline them, though many gemini browsers allow auto inlining of images. There is no specific line format for them, they are just another link line pointing to an image.