lost images / broken links / managment?

I need to clean up the thousands of images in my /images folder and I suspect this might result in a few images becoming ‘lost’ to the site. How does WP deal with this? (Lost images don’t seem to show up on front end pages – WP just ignores them)
Is there a plugin or hack that can flag up ‘lost’ images so that I can manage and make any corrections necessary.
Thanks for any assistance.