This is a plugin designed to do one simple job: programatically add a featured image in WordPress to existing posts.
I've worked on a couple older WordPress blogs which had hundreds of posts in the old format, where Featured Images wasn't really a 'thing'. Adding a new Featured Image to each one would take days of effort. With this plugin, you can quickly and easily use either the first or last image from within the post to be the new Featured Image.
https://github.com/foghorn/fibs
https://wordpress.org/plugins/featured-image-bulk-set/
No one here is claiming that this is the best or prettiest way of doing this. But it's here, it works, and it's free.
- Download this code and install it in your wp-plugins folder
- Activete the plugin in your WordPress plugin section of the wp-admin panel
- There should be a new section called "FIBS Menu" added to the Settings section. Click that.
- Select your options and hit "save" to start the process. NOTE: this process cannot be stopped once stared.
- NOTE: If you don't click the box at the bottom, you can do a test run of the process to see what the result will be.