Yes, you should cite all sources. Just because something is no longer copyright does not mean that you can use it freely. You can be accused of plagiarism if you use it without citation.
It is permissible to use a copyrighted image if you cite the source it came from.
how should you show that a piece nof work is copyrighted
Only if the copyright is not part of the copyright registration that is copyrighted in the publication of the author's registration. But If the copyright is part of the copyright registration that is copyrighted in the publication then the copyrighted author of which publicized the copyrighted registration is not copyrighted in the legalized sense of which a publication is copyrighted. Yes, a work is always copyrighted, before and after editing and both versions.
Anything new that someone writes can be copyrighted. Technically a work is automatically copyrighted once it is created unless the author explicitly abandons copyright in the work.
It is okay to write a book on something that is copyrighted, but you cannot publish your work unless you get permission from the author.
Permits the use of copyrighted work.
Anytime you use the work of someone else, you cite it. If you do not, then it is plagiarism.
The entire novel is copyrighted. While one cannot technically copyright a title, the book is a copyrighted work. The holder can bring suit against anyone that violates their rights.
The only way a work created by you can become 'not' copyrighted, is if you've voluntarily given up those rights.
Ideas are not subject to copyright protection; only the expression of the ideas.
While fair use allows for limited use of copyrighted material without permission under certain conditions, it is still recommended to cite sources when using them in your work. Citing sources helps give credit to the original creators and prevents plagiarism, even if your use may fall under fair use guidelines.
Yes. Computer code is protected as a literary work.