Right now there is a bit left to be desired when it comes to lemmys accessibility features, but it’s a good idea to be mindful of the fact the fediverse and its platforms tends to have pretty universal accessibility features that will likely come to lemmy sooner rather than later
I can’t really think of a case where a post’s image isn’t relevant to the associated discussion. Even if it’s just a nonsense post with an unrelated image, knowing what the irrelevant image is about would help make sense of the discussion.