| add_image_size() | Register a new image (thumbnail) size. |
| delete_post_thumbnail() | Remove a post thumbnail. |
| get_intermediate_image_sizes() | Gets the available intermediate image sizes. |
| get_post_thumbnail_id() | Retrieve post thumbnail ID. |
| get_the_post_thumbnail() | Gets the IMG tag of the post thumbnail (if exists). |
| get_the_post_thumbnail_caption() | Gets the post thumbnail caption (description). |
| get_the_post_thumbnail_url() | Return the post thumbnail URL. |
| has_image_size() | Check if an image size exists. |
| has_post_thumbnail() | Check if post has an image attached. |
| image_get_intermediate_size() | Retrieves the image's intermediate size (resized) path, width, and height. |
| remove_image_size() | Removes a previously registered image size by it name. The new image size is registered with add_image_size(). |
| set_post_thumbnail() | Set a post thumbnail. |
| set_post_thumbnail_size() | Registers an image size for the post thumbnail. |
| the_post_thumbnail() | Display the post thumbnail. |
| the_post_thumbnail_caption() | Displays the post thumbnail caption. |
| the_post_thumbnail_url() | Display the post thumbnail URL. |
| wp_get_additional_image_sizes() | Gets data of all additionally registered image sizes (thumbnails). |
| wp_get_attachment_thumb_url() | Retrieve URL for an attachment thumbnail. |
| wp_get_image_editor() | Returns a WP_Image_Editor instance and loads file into it. |