At the time of inserting a post I can select some images to include, as a prominent image, images in the body of the post and also by fields created by plugins (eg Advanced Custom Fields). These images can be resized with the add_image_size function in the functions.php file of the theme, for example.
However, how can I add different and specific (plural) sizes for the featured image, for body page images, and for the images of these new created fields?