What means when a graphic generates 404s?

Hi:

I’ve implemented Better WP Security and now I’d like to better understand some things. There are a couple of graphics in my theme, all background graphics, that come up over and over in the list of 404 errors. I don’t mean they fill the list, but pretty much every day they appear at least once. They are all “working” on the site in that they show where they should, when they should.

I understand the idea of someone trying to find a nonexistent page or a page that has been moved or just making an error (such as using .htm instead of .html, etc.) but I don’t understand a theme graphic generating an error message.

Appreciate any info – thanks!

http://wordpress.org/extend/plugins/better-wp-security/