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The books I've investigated had a text saying "This copy belongs to: %s" where %s was an email address at the beginning, and an invisible hex string at the end
by miki123211 8y ago
The books I've investigated had a text saying "This copy belongs to: %s" where %s was an email address at the beginning, and an invisible hex string at the end of every chapter. The string had a width and height of 1px, so most conventional readers didn't show it at all.