If drag and drop is your preferred method to add content to the WordPress media library and you’d like to extend that functionality to the featured images meta box, you’re in luck. Developed by Jonathan Lundström, Drag and Drop Featured Image adds the ability to drag and drop images into the featured image meta box when writing a post.
Since the plugin utilizes the default functions in WordPress, the meta box compresses all image sizes as well as respects any custom image sizes. If you’re using WordPress 3.5 or lower, the page will refresh in order to show the new image. Newer versions of WordPress show the new image without reloading the page. The plugin works as advertised without any issues with WordPress 3.8.1
Drag and Drop or Select Files?
I rarely use the drag and drop method for two reasons. First, both monitors usually have a full browser window meaning I’d have to reduce its size in order to access the media files and drag them into the window. Second, since I’m already working within a full size browser window, I find it more convenient to select multiple files using the select files feature in the media library. Let me know in the comments why you prefer one over the other or why you use both.
Drag and drop, without a doubt. On Mac I use an app called Cinch which lets me whip the window out of the way and maximize it again easily.
Sadly I had to drop the Drag & Drop Featured Images plugin, because it had a very annoying bug. The popup modal doesn’t allow you to filter the images to only show those attached to the specific post. Minor? Yes. Annoying when you’re editing posts from several years ago? Also yes.