Comment on Stallion WordPress SEO Plugin by SEO Gold Services.
The random thumbnail feature is similar to the random banner image feature, only difference is there’s two sets of images 100px by 100px and 200px by 200px. The 100px images are used by widgets and the 200px images used for thumbnails within archives. Both versions are hooked into Timthumb.php so bandwith usage is minimized, which is why the Stallion cache folder (/wp-content/themes/stallion-seo-theme/cache/) is so important to have the correct permissions set otherwise Timthumb can’t create the smaller thumbnails.
With regards permissions 777 is a potential security issue, always start with the minimum permissions needed and work your way up, on some servers 755 is enough, others 775 and what should work (as last resort) with all 777.
I have sites on the same server where 755 works and others 775 (never needed 777), probably a case of building the sites on different servers years ago and some settings being inherited as I used a backup to move a domain from an old server to a new server.