Most Fediverse software supports image uploads, so there’s no reason to use Imgur for image hosting. Hell, even on my small single-user server (atomicpoet.org), image hosting is easy peasy. Not only is Imgur not needed, they’re an annoyance for those of us who are used to seeing images natively on the Fediverse.
I know habits are hard to break, but just remember: this isn’t Reddit 🙂
On Mastodon, like kbin and lemmy, locally posted images are hosted locally, and remotely hosted images are cached locally. This can cause a lot of storage. But you can run an automated cron that will clear out cached images older than whatever you want, like a month. Then the local cached storage is at a minimum, and if someone wants to view the image again, it’ll get fetched. I don’t know if kbin and lemmy have this feature, but they should. It’s probably not the locally uploaded images that’ll take up a ton of space, it’s caching all the remote ones that will.
Note that not all instances do this. Especially not necessarily if they aren’t mastodon. My calckey instance for example has it optional and i have it off there. Akkoma i know also can do it optionally.