I might have prior art on this, circa 2002; the original code didn't survive but I have an online posting detailing it. An ebook water-marking script in Perl w

I might have prior art on this, circa 2002; the original code didn't survive but I have an online posting detailing it. An ebook water-marking script in Perl which edited the book meta-data (index, contents, preface, indentation, position of page numbers, fonts sizes, colophon and other stuff to generate unique "on demand" copies of texts that could identify the buyer.