Interesting. So could I publish a modified book, by publishing a piece of software, that transforms a known book into a new book. Then the user would be doing the modification.
Would that not be legal, as long as my software doesn't contain pieces of the original book copied verbatim?
IANAL (and in the EU) - I believe you're not allowed to republish/redistribute the modified copy of the book. That said, your software is still legal for an end user to use on any book they own.
Same thing here, if the modifications were happening on the server side and then sent to your browser that's probably not legal
You can sell software that decompiles, disassembles and recompiles software. Same thing with software that manipulates and edits existing copyrighted videos.
Publishing it, however, is where copyright law kicks in. Publishing is a specific right that you need to be granted by the rights holders.
I don't see how software running on a client's computer that changes rendering of copywritten work is the same thing as publication. Browsers, video players and Adobe's products all allow users to view and modify copyrighted works on their machines, and that isn't publication at all.
You can in some cases. Copyright law varies from country to country, check with a lawyer if you need advice, and all that... If what remains of the copyright work is less than 10% then your copy is legal. When you modify something it becomes a derived work, the question is when you have modified it enough that it is considered a unique work and not derived.
Note too that trademark law can still apply. So your Harry Potter can be in trouble even if the only thing that remains is the name and the universe. (You can do a Harry Potter as the horse in your western novel)
This comment is misleadingly reductive of complicated questions of both Copyright and Trademark, I suggest you take it down to avoid misleading people. Parts of it are blatantly incorrect under U.S. (majority of readership here)[1], other statements "you can do a Harry Potter..." are conjecture that bury the actual legal question a court would consider (likelihood of confusion), and no lawyer in their right mind would offer such a unconditional opinion without knowing specific facts of specific cases.
Would that not be legal, as long as my software doesn't contain pieces of the original book copied verbatim?