“Is material published in the Internet Public Domain even though the material has come from books published after 1923?”

There’s a lot of possible answers to this question and the answer would depend on the specifics of the situation but I’ll give you a scenario and you can tell me if it’s close to relating to your question.

Let’s say a person took a book published in the U.S. between 1923 and 1963 and…

This book was NOT renewed for copyright protection 28 years after publication…

Then under U.S. Copyright Law this book would be in the Public Domain.

Let’s then say that this person posted the book somewhere on the Internet.

The original content of this book will always be in the Public Domain.

If this same person added additional original material to the book, then this additional material would be protected by copyright but NOT the original Public Domain parts of the book.

Once in the Public Domain, always in the Public Domain.