It's both: a copy of the original (but, critically, a copy made by someone with authorisation to make copies) and a copy of your work, which you executed yourself.

You have the right to sell both, one as owner and one as owner and creator. But you only have the right to make reproductions of your own work, which means if you want to make more copies of the complete derivative, you have to buy new authorised copies of the original. You don't have the rights to make your own copies of the original to modify and sell.

> and a copy of your work, which you executed yourself.

But the copyright on derivative works is held jointly by both authors.

Do you have any citations of case law backing up your interpretation? I'd be really curious to see if a court has actually ruled on this.

The copyright on the whole derivative is joint, but the the copyright on your contribution only is yours[1, p26]. If your creative input relies on the original (e.g. you interliniated a Harry Potter fanfic into a book), you won't be able to sell only your contribution, because the original copyright includes the characters and so on and extends to your work. However, if you draw decorative borders around each page (that are not based on the original: no Ravenclaw logos!) you could photocopy the pages, isolate the borders and sell them separately, but you could not make copies that included copies of (or copies of derivations of) the original text.

As for the sale of the physical modified-but-uncopied original itself:

In the EU, this is permitted under the equivalent to the first sale doctrine[2, p880][3, footnote 7], which covers all IP, including trademarks and patents. There's now some weirdness around Brexit which is what document [3] is all about.

The case law actually goes both ways in the US because the concept of derivative work is not conclusively defined in statute:

* It's OK: Lee v. Deck the Walls, Inc. [4] aka Lee v. A.R.T. Co.

* It's not OK: Greenwich Workshop, Inc. v. Timber Creations, Inc. [5], and also Mirage Editions, Inc. v. Albuquerque A.R.T. Company

These cases are almost identical and one on each side even involves the same defendant, but have opposite conclusions. So as usual, the US gets weird and jurisdictional with it. So, indeed, my original comment is actually wrong in that US First Sale Doctrine isn't guaranteed to apply and mostly seems to depend on the circuit you get sued in. TIL.

There are additional rules if the original is limited edition or certain types of art (usually "visual" and "limited"):

* In the US, VARA means certain creators can, in some cases, sue for damages if you destroy or modify their work, even if you own it

* In the EU there's the Resale Rights Directive (which codifies what is often called droit de suite) which gives royalties of each sale to the artist (but this right cannot be transferred or inherited)

[1]: https://www.wipo.int/export/sites/www/sme/en/documents/pdf/i...

[2]: https://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1...

[3]: https://ec.europa.eu/info/sites/default/files/brexit_files/i...

[4]: https://law.justia.com/cases/federal/district-courts/FSupp/9...

[5]: https://casetext.com/case/greenwich-workshop-inc-v-timber-cr...