Image links automatically converted to attachments?

[delmarva]

I am having a problem with members posting their images using the old "Hot Link" method. While this steals bandwidth from other site's servers, I also lose a lot of the thread related content when that server moves it's images or goes down. I get the dreaded "red X"

Does anyone know a way these images could automatically be converted to attachments and saved on my server? Could there be such a cron job?

Thanks for the help in advance.