[manfeed]

Can the skin code detect if there is an image to show, and choose not to show it if there is nothing? I'm guessing somewhere it is picking a random number and finding the artwork for movie number #random. Can it check to see if such an image exists and move on to the next one if it does not exist?

No, sorry, that's not possible, since that option is provided by a script, not by the skin itself.
I would recommend to create a folder and put there a good amount of fanarts from your movies and when choosing the background for movies in the home menu select 'multiple images' and point to that folder. That's what I do, since that has the advantage that you can show the best fanarts, the ones that you like most or are of a higher quality.