It's not big deal, you can use random php function. Where would you like random image to appear? There are some plugins for this.
Can you show an example ? Do you mean like the Featured Article section in some blogs ? or changing the image of the same post ?
That's a custom design by this guy http://www.epicwebstrategies.com/, so you'd have to call him and hire him to do it for you. Here is a plug in that has a similar function of fading featured post images: http://wordpress.org/extend/plugins/dynamic-content-gallery-plugin/