HTTPS and Secure Content
Https is a protocol that encrypts the data going to and from a website so that other people can't easily read it in transit. (Note that it has nothing to do with the trustworthiness of the website's content.) It is rapidly becoming a requirement to use https for everything.
Modern browsers will give a warning in the location bar if you access a site over an open or unencrypted (http) connection.
These two images are from Firefox and a Chrome-based browser.
Modern browsers will also give warnings when you try to enter a password into a webpage which uses plain http. These two screenshots are from the same two browsers.
You may also get a warning if the website contains mixed content. In this context, it means a mixture of "secure" or https content and plain http content. Many modern browsers may refuse to display the http content at all. This means that you'll see blank areas instead of the image or other content.
This is a YouTube link using http, leaving a blank area in some browsers.
This is the same page, but with the YouTube link set to https.
If you use the WYSIWYG editor to insert images, you won't have a problem. (It uses a "relative" form of the link, "/imageuploads/clubnumber/imagename", which works equally well with http and https.)
You are more likely to have problems with content imported from other sites. Examples include images hosted elsewhere, and embedded videos and iframes where content from another site is displayed directly in a window in your own site.
In this image, the link begins with https (circled in red) and it displays correctly when the site is accessed over a https connection.
If you are finding blank areas in your site where items are refusing to display, check the pages carefully for http links and change them to https.
In a few cases, if the site you're linking to doesn't use https, you get a error message and the content still won't display. Unfortunately, there's not much we can do about that.
A http link to another site in your public or members-only menu isn't affected by these limitations and should work without any problems.