UPDATE: Now supports externally hosted images.
UPDATE2: Externally hosted images generation was improved.
WordPress 2.9 introduced the new feature Post Thumbnails. This feature allows to assign post thumbnail at post Edit page for each post, specify post thumbnails sizes in theme settings, and easily call post thumbnail of specified size in any place of the theme. Read more information about this feature at Mark on WordPress – New in WordPress 2.9: Post Thumbnail Images
The plugin Generate Post Thumbnails helps to automatically create post thumbnails for existing posts using post images. This plugin by default takes the first image in the post content and assigns it as a post thumbnail according to specified settings in the theme.
I found this helpful after I decided to use Post Thubmnails feature in existing WordPress blog. I upgraded my WordPress to 2.9 and altered my theme settings according to New in WordPress 2.9: Post Thumbnail Images. I had hundreds of posts already, so I needed an automated script to run through them and assign my first post image as a post thumbnail. This is when this plugin came in handy. It is working using Ajax requests, so there is no timeouts issues. For my 200 posts it has been executing for 4 minutes. Anyway, this is faster than to do this process manually.
- WordPress version 2.9 or higher
- Theme should support Post Thumbnails. Read here how to enable this feature in themes New in WordPress 2.9: Post Thumbnail Images
- Download plugin
- Extract zip in the /wp-content/plugins/ directory.
- Activate the plugin through the ‘Plugins’ menu in WordPress.
- Open the plugin management page, which is located under Tools -> Generate Thumbnails. If you get plugin warning, that means either your theme does not support WordPress Post Thumbnails feature or your WordPress version is lower than 2.9. See related links for more information.
- Set Overwrite parameter, if you want existing post thumbnails to be overwritten by generated thumbnails.
- Set the number of the post image, that you want to be used as your post thumbnail.
- Click on Generate Thumbnails and wait until process is finished.
- After this plugin assign all post thumbnails I suggest to use Regenerate Thumbnails plugin if you changed your media settings or theme post thumbnails settings and need to regenerate new thumbnails.
More useful plugins:
- Regenerate Thumbnails -Â recreates already existing post thumbnails after changing their settings; however, it does not assign them if the post has no thumbnails yet.
- Auto Post Thumbnail – generates post thumbnail after post saving.