Originally posted by Katerpie
It's a simple matter of changing http:// to https:// to make the image secure again
No, it's not. First of all, the site has to support HTTPS in the first place (most common servers such as Apache and Nginx do allow you to use HTTPS connections and even force them with redirections if set up correctly) and Browsers still may have trouble if the connections is uncertified or the certificate ran out.
Edit: Added more information about HTTPS and the webserver.
Okay, my layout looks ugly.