With our latest update (3.1) to the Mu theme, the theme will no longer be shipping with the timthumb thumbnail script. By default the theme will now use the native WordPress thumbnails requiring users to add a feature image to each post or page.
Adding Feature Images to Posts and Pages in the new Mu
To set the image used by the theme for each post or page you must set a feature image in the WordPress post/page editor.
We recognise that there are lots of Mu users out there who have been using the theme for maybe a couple of years. Don’t panic – we have left support for the script in the theme.
All you need to do to reinstate timthumb and have it pick up all your post images again is to download the latest copy of the timthumb script from the official source here and drop the timthumb.php file into the themes \thumbs folder.
And all you need to do to ditch timthumb is delete it! The theme will then revert to WordPress native thumbs when timthumb is not present.
Switching Your Existing site to WordPress thumbs
So if your are upgrading from a previous version, you must delete the timthumb script or even the whole thumbs folder in order to benefit from the WordPress images. But you will also need to go back through all your old posts and set a feature image for each.
We hope this doesn’t inconvenience existing users too much, but timthumb has in the past represented a security vulnerability and while the latest version overcomes these issues, we have long recognised that the script offers few advantages over the native thumbnailing introduced into later versions of WordPress.
Our more recent themes do not use timthumb at all.