The first picture is of a BIG BOOK. They are used for large groups so that everyone can see the pictures. They are ideal for circle time activities.
This second picture is of a BOARD BOOK. They have thick pages and are easily wiped clean. They are ideal for children under 2 years old because they are easier to hold and turn the pages.
This final picture is an average sized PICTURE BOOK.
This is the size you normally find in the children's section of the library.