Yeah, what @jon2 says. And here is a post by me after “discovering” how images are handled behind the scenes…
It’s important to understand, though, that the “master” image in Bubble’s AWS storage is what counts toward your app’s quota. As such, if you have an image-centric website (e.g. photo sharing or the like), it would make sense to downsample the image before it’s uploaded to your Bubble storage. My Upload Buddy plug-in does this. It’s super lightweight with no external dependencies. There’s also a more full-featured (but heavier) plug-in available as well.
Just FYI, the master image should not be deleted, because it’s used to [re]generate all the context-optimized versions of the master image across your site.
-Steve