Well here is a plugin that will randomly pick an image that you upload through your back office media interface.
You just have to make sure the file name begins with a [EW-] (for Use Feature) and it is unattached. Just upload it and don�t use it for a post.
The Advanced Photo Gallery is a very simple wordpress plugin that embed a gallery anywhere on your site.
This plugin was built to download and set the featured image of a thumbnail for specific video source embeds. Currently supported video sources: YouTube, WordPress.tv
Shortcode allowing a floating featured image to be placed at the top of a post; this plugin is multi-site compatible.
Seamlessly adds featured images to your RSS feed with customizable sizing options.
This plugin automatically sets featured image for your blog posts if post thumbnail is not set manually. This extracts keywords from your article title and content and searches for image in pixabay.com.
Search for free or creative commons images from your media manager. Great for finding featured images or photos for your blog posts.
Automatically sets the featured image to the first image uploaded into the post (any post type with thumbnail support). So easy like that...
Set images for categories and tags, especially for fallback post thumbnails or featured images.
Featured Image For Custom Post Type Plugin Is Show Featured Image in All Post Section.
Generate Featured Images automatically based on your post content (title, etc). Customize your featured image with the built in template editor.
Simple plugin for creating sliding door CSS sprites out of uploaded images with a range of image effects.
从内容的图像自动生成特色图像。
Builds post widget based on options you choose from a form in a widget
Download Featured Images will allow users to download featured images.
Allows the custom header image to be replaced by the featured image of the current post or page.