There's been a recent incident that I have come across (https://musicbrainz.org/search/edits?auto_edit_filter=&order=desc&negation=0&combinator=and&conditions.0.field=editor&conditions.0.operator=%3D&conditions.0.name=Deleted+Editor+%232244710&conditions.0.args.0=2244710&conditions.1.field=type&conditions.1.operator=%3D&conditions.1.args=314) wherein someone had spent many hours fiddling with artwork (upscaling it, touching it up) for their own benefit and then replacing or uploading that artwork to releases.

A respected community member (aerozol) stepped in and advised against this and the original editor got upset that they had spent their time and has since gone nuclear

We've had similar issues in the past wherein contributors are spinning in their own circles not realising they're breaking the project rules, as not everyone will read through all of the docs.

At the moment this document exists (https://musicbrainz.org/doc/Cover_Art) to explain that we dont accept edited or fan art, but it's not an official guideline. But I am of the belief that most long-term contributors understand this is a rule. Maybe that rule needs to be added to the official style guide or similar, and then on the "Add Cover Art" page for a release (https://musicbrainz.org/release/*/add-cover-art) maybe above the edit notes box there should be the guideline printed clearly to state what should/should not be uploaded.

Roughly it should read:

Before submitting your artwork please ensure it is relevant and accurate to the release selected (for example check release identifiers such as barcodes and catalog numbers). Please also be aware MusicBrainz expects original artwork to be uploaded to the Cover Art Archive (CAA) - artwork that is fan-made, or has been extensively modified to remove elements of the image are not accepted.