The Gemini protocol does not mandate lack of images. It is simply left up to the implementation to decide how (or whether) to display those.

One of the most popular Gemini browsers, Lagrange, shows images inline once downloaded. But you need to click their link to ensure you want to see the content first.

E.g., view this in lagrange to see what I mean: gemini://8by3.net/~xkcd/