How to add a thumbnail to a wordpress post if the images are originally in a sprite?

Question

WordPress

Added a post using the function add_theme_support( 'post-thumbnails' ); . But initially I have 4 posts screenshot.ru/80f1197284a4ac7892b20b384d1bc362 (as I understand these posts) and they have different pictures sewn into one sprite. How do I deal with thumbnails? Add a separate image to each post? But why was it necessary to make them a sprite ....