Insecure content on a secure page
I've been setting up domain registration on my site and it's done through the registrar's secure pages (https). However, the header and footer I use to customize it to match my site pull images from my server (http), which does not have a secure area.The problem with this is that every time I pull up a page, I get a message saying "This page contains both secure and nonsecure items. Do you want to display the nonsecure items?" Of course, that's rather annoying and I can't put a customer or potential customer through having to click "Yes" or "No" with every page change.
Do I need to obtain a certificate and create a secure area on my site, or is there another way I can make that message stop, not only for me but for anyone else trying to register a domain through my site? Any suggestions will be greatly appreciated.