Some people find book jackets, aka dust jackets or dust covers, annoying, but most librarians want to keep and protect these covers on the books that have them for several reasons.
A Brief History of the Dust Jacket
Library Technology NZ
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Dust Jackets - Specialties Graphic Finishers - Book Binding
How to cover a library book
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Dust jacket - Wikipedia
3 Ways to Cover a Paperback Book With Clear Plastic Film - wikiHow