I am looking for a way to generate featured image per post based on the first image in the post for old posts without a set featured image. I'm switching from handmade thumbnails to auto generated featured images. With new posts I got this working, but I don't want to set a featured image of my other 2000 posts by hand. Found some plugins, but they aren't working well or not supported and the info I did find here is all about setting the image with new posts. Any hook, script or function for this? Anyone got an idea?
You can look into this post: http://ken.ph/first-image-of-wordpress-post-as-thumbnail/
Or if you're comfortable with MySql try using this (obviously check it on local database first):