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.
Plugin converts Cyrillic, Georgian and Greek links and file names to Latin characters. This is essential for the accurate WordPress plugin operations, and visibly improves the readability of links.