The International Standard Book Number or ISNB is a number given to a book and often placed on the back cover to protect the book from the plagiarism & quotation. It guarantees the copyright for the author & the publisher because this number is unrepeated ever like the fingerprint!
By ISNB, you can verify your intellectual property, if someone plagiarized your ideas.
But as usual, getting this local number is a costly thing and takes long procedures.
After the digital or electronic publishing & eBooks became widespread on the internet, Digital Rights Management or DRM appeared.