A plugin for updating your thumbnails whenever a new thumbnail size is added with add_image_size()
Installation is easy. Unzip into your wp-content/plugins directory and activate. Thumbnail Updater can be accessed through the Media Library. Navigate to Media Library, click on any image and you should a button that says "Update Image Sizes." Clicking on that will open a popup that lists all of the available image sizes. If a thumbnail size exists for that image, there will be a check next it. If the thumbnail size doesn't exist, then a red exclamation mark will appear.
thumbnail-updatefolder to the