All of LibriVox’s audiobooks are in the public domain.
Project Gutenberg, while mostly focusing books also has some illustrated books, music, videos, and pictures on there.
Public Domain means you can use it for any purpose including commercially.
What might be happening is that some people/companies claim copyrights to their copy of a PD work. Eg someone takes a photograph of the Mona Lisa, and while the painting is public domain, they own the copyright to their photograph, so you can sell an image of the Mona Lisa but not their image of it. With text, perhaps someone might claim this of their OCR version (effectively copyrighting their typos and transcription errors). A translator has copyrights to a translation they make of a PD text.
Another thing that can happen is that a company/source/website uses boilerplate copyright language for everything on their site/publication, so their boilerplate says you can't do this or that but it doesn't quite apply to everything on the site because there is some PD material on the site. On a sleazier level, a company business model might be to deceive people into paying for the right to use material that they're not aware they actually already own as common heritage and can already use freely.
In your case, as long as you know the texts are in the public domain (ie you're not just taking some website's word for it that their content is PD), you know you have the right to use it. Project Gutenberg has some clear-language easy-to-follow guides for determining if a text is in the public domain, and is an all-round excellent resource for these kinds of questions. (Though it mostly focuses on USA law).
I believe so!
I wanted a new copy because I bought the 2005 reprint back when that was published and wanted a newer larger copy (the '05 printing was pocket book size). It appears it was reprinted in 2018 as a tie-in to the Broadway musical adaptation, which specifically at the time cited the book as the source material.
I compared my '05 copy with the newer one and the text appears to be the same. :)
Here's the one I recently bought: https://www.amazon.com/gp/product/081297493X/
Not weird at all, but very tough. Many, many versions exist. The thing to watch out for with most of them isn't the original text, but the alleged "copyright" status of the translation.
I looked only on Standard Ebooks, and found only one item. While Standard Ebooks is certainly no one's attorney or legal advisor, they're thorough and reasonably careful; mainly, they just turn out excellent work.
You tell me you can't use the name in the interior or exterior, but like, even releasing the existing public domain material people use it. I can't well adapt a Sherlock Holmes book if I have to call him Herlock Sholmes all the time, ah?
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Getting back on the topic of my project, here's my thinking: If I am working on a Wonder Woman comic after it becomes public domain, and I introduce a character I made called White Swan, DC might say "ok, buster, Wonder Woman is one thing but you definitely can't use Silver Swan, or a knockoff of Silver Swan, yet."
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But! If a character happens to exist in creative commons called that and with a sort of similarish story(but that doesn't directly infringe and doesn't mention Wondy or any other copyrighted DC materials), and you happened to use that character, that you didn't create, in conjunction with Wonder Woman, which is in the public domain, like I figure they wouldn't be able to do much to you. They would have had to sue the original maker of the character which they won't because they can't prove they intended this character being used this way. They aren't gonna sue you NOW for making a small page saying you are releasing White Swan to CC, and by the time people can work on Wondy it'll be too late! /That's/ why you do this now, 13-15 years before.