I don't see what I'm not understanding. I'm not talking about attachments. The image proxy is used to avoid mixed content warnings on hotlinked images, it is not used with attached files, as it is not needed. It sounds like your images broke on that other site because they ran some sort of database query changing the URL of all images to HTTPS. We don't do that here, what we do is we proxy the images through our own server, so the page loads as secure. It actually wasn't enabled here, but it's enabled on BYC. I just enabled it here, and now you can see that the page loads securely, despite the hotlinked images from your non-HTTPS site, because the images are proxied through this site.