Remove them or change their name where they're hosted. This is what I did to many of my most popular image links I had hosted at roadie.org, especially in case I fell out of favor with the owners of the OS. Then you have to change the links anywhere else you posted them. If you gave the images to the OS by posting them as attachments, you may have to go through the DMCA takedown process. I'm sure you can google for that.