Automatically create human readable labels for custom image sizes created with add_image_size() so that they’re selectable in the WP admin. For example, when you insert media into a post, in the Attachment Display Settings->Size select list, your custom image size will now be available. The plugin uses the image_size_names_choose filter as described here in the For Media Library Images (Admin) section. By default the human readable name is the ‘name’ variable given to add_image_size() stripped of non-alphanumeric characters and the first letter of each word in uppercase.