There is a report that shows abandoned files. You can delete them manually. A bit of a pain, but there is little other way to be sure that something isn't needed.
Direct upload to server
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I want to upload Images, and Videos on my server, directly. (not Imgur)
Is this possible? -
Not yet but it is on our list of things to do. https://github.com/designcreateplay/NodeBB/issues/563
closed Saving uploaded images to disk vs Imgur #563
