Actually I can't really bash #Lemmy for this (as much as I'd want to) because it seems like pretty much the rest of the #fediverse has this problem of images not getting immediately removed from the server when you delete the image or even your account. I've tested with #Mastodon, #Pleroma, and #Misskey (even Misskey somehow gets it wrong by not immediately making your image unavailable by the URL even if you've deleted it from your Drive, however this doesn't always happen, see below).
Now I'm not sure about instance admin stuff (and I haven't tested with my admin hat on in this Misskey), but I'm guessing you don't have a view of all uploaded photos by a user that an admin can delete from in Mastodon and Pleroma either (please prove me wrong though!). :sagume_think: Misskey does let you view all files uploaded by a user and delete from there, though I'm not sure if the file gets immediately removed from the server once you hit delete, but it's probably gonna be like what I'm going to write below
What I do know about Misskey is that, if you've never accessed the URL generated for the file in your Drive, and hit delete, the next time you access it, it definitely will no longer be available; a pure 404 as expected. However if you've accessed the URL at least once, then the file will get cached. I'm not sure if it's Misskey doing this or the reverse proxy (like #nginx), because clearing cache or switching to a whole 'nother browser still shows the file is available.
Oh, and have I mentioned that all three software will automatically put your image into the server the moment you hit the upload button, even if you haven't submitted the post yet? Yeah it's equally as easy as Lemmy to accidentally upload something to those three as well.
