Which innovative book packaging design, introduced in the early 2000s, revolutionized the romance novel industry by concealing provocative covers and helping reduce reader stigma?

In the world of book publishing, packaging design plays a crucial role in attracting readers and conveying a book's essence. From dust jackets to special editions, publishers have experimented with innovative packaging to make books stand out in increasingly competitive retail environments. This trivia question explores a groundbreaking packaging innovation that changed how certain books were marketed and consumed.

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The reversible dust jacket (allowing readers to flip between a traditional romantic cover and a more subtle, abstract design)
The transparent slipcase (displaying only the book title through clear plastic while concealing the actual cover art)
The customizable cover template (where readers could download and print their own book covers)
The digital wrapper (books sold with a QR code allowing access to alternative cover art online)