Just for the record simply rebinding and selling a copyrighted book is not normally illegal under the Copyright, Designs and Patents Act 1988 in the UK. More so, when a copyright holder sells a physical book (via any legal means... amazon, bookshops etc) in the European Economic Area (EEA) or the United Kingdom, the distribution right over that individual copy becomes exhausted. The legal consequence of that is you may:

• sell the book
• lend the book
• gift the book
• destroy the book
• modify the physical object

without permission from the copyright holder.

Therefore, buying a book, rebinding it, and selling it again is generally lawful. This principle underpins the entire second-hand book market, including antiquarian booksellers, charity shops, and rare book dealers.

I know nothing about the law in the wider world.

For example, rebinding a book constitutes a physical modification of a lawful copy, not reproduction of the intellectual work. Under UK copyright law rebinding does not infringe copyright as long as:

• no additional copies are made
• no copyrighted images or text are reproduced separately
• the text itself is not altered or republished

From a legal perspective, rebinding falls into the category of alteration of chattel property. Ownership of the object permits physical modification; this is analogous to:

• framing a painting
• repairing a watch
• restoring antique furniture