Thank you for your response ecommerce. Some of my image folders are empty - could that be the problem? These were pre-loaded images that were present after my initial install. They had nothing to do with my products.
I could see where some of the deleted images are used for blocks or templates that are not being used by my store. Like I said before, these error messages do not seem to interfere with my store's operation.
When you say "admin", do you mean the admin sub-folder under public_html? If so, what do I look for there? I have never changed any file or folder in the admin area.