You can easily display a set of given number of random images from your WordPress site’s media library. Random Images is the new WordPress plugin that activates a simple shortcode you can use in your website’s shortcode supported areas like posts, pages and text widgets.
Installation & Usage: Install and activate the Random Images plugin then use[random_images] shortcode for displaying random attached images from published posts.
By default the plugin shows 6 thumbnail size images but you can easily set the number of images and use a custom size as shows below:
[random_images total=4 size=medium]