"Picture cover" is a common term among book collectors. Many early series books and later children's books have this binding, as do most modern textbook

Textbook

A textbook or coursebook is a manual of instruction in any branch of study. Textbooks are produced according to the demands of educational institutions...

s.

It is a method of bookbinding

Bookbinding

Bookbinding is the process of physically assembling a book from a number of folded or unfolded sheets of paper or other material. It usually involves attaching covers to the resulting text-block.-Origins of the book:...

 that preserves the contents as well as a normal hardbound book, but has the visual appeal of a paperback book.

The pages are collated, stitched and trimmed as for hardbound, but a cover with a picture on it is attached instead of the normal hardbound cover with printing on the spine — and perhaps front.

A hardbound book can achieve a similar look with a dust cover, but the cover is fragile and inconvenient when reading, being most useful while the book is shelved.