If you set featured image for every post. You are wasting your lots of time. Because this process can be automated by this plugin. This plugin selects the first image from the post and set the image as featured image automatically. You just have to insert the image into your post. If you want to set featured image manually, it won't interfere in that case. Your selected image will be set as featured image.But remember, it will work for new POSTS only, not for the older one.
Currently this plugin is tested with latest wordpress version 3.5.2.
1. Download the wordpress-automatic-featured-image plugin and extract the "wordpress-automatic-featured-image" folder.
2. Upload `wordpress-automatic-featured-image` folder to the `/wp-content/plugins/` directory
3. Activate the plugin through the 'Plugins' menu in WordPress
4. That's it. There is no further options page.