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.
There's a new version of aVideo called Smart Video, which is better for you to share videos. For WordPress 2.5.x to 2.8.x, it's recommended to update to Smart Video.