Even on a slow connection, if you’ve clicked the link, you’re there to view the post. The image simply must be visible by default. It would be more interesting to allow clients to choose what image quality to load, but I don’t know a good way to do that. Maybe default to low quality, then you can choose high quality after logging in?
Eh, if you’re mostly just consuming/lurking, it’s probably better to use Lemmy by viewing all posts on all communities on all instances, then filtering out the communities you don’t like. Gonna be like that until it gets more popular, and importantly, stops becoming less popular.