I had a fun time tracking this down. Every time I would copy/paste a link from a site's blog, the title would display, the link would display, but the images would return nothing. The link was correct and clicking the link would take me to the correct post. I went through my settings in NSM Better Meta and included all of the recommended OG meta tags, but still, nothing.
What I found was that by changing my URL of Upload Directory from just "//" to "http://" fixed the issue. That's all fine and dandy, but it doesn't help me keep relative protocols for images. I have both http and https on this site in different locations. It also depends on where they are coming from and if that section of the site has a link that was entered as https. (Not under my control)
Is there any way to set a relative path in the URL of Upload Directory field and have the templates render the path with the protocol from the address bar used?
EXAMPLE:
This renders as:
Which is correct. I can switch from http: to https: without issues of mixed content.
When I copy the link and paste it in FB, the issue is seen:
NOW...
Change over to the http: or https: in the settings...
This renders as:
Which is correct, but not what I want...
When I copy and paste this link into FB, I am given the images...
THIS is why I am confused....