I figured it out after about 15 seconds from seeing one of the images load on-demand. Which is the time any self-respecting computer programmer should take.
I load links as background tabs and visit them later when I am on a slow connection. When sites do things like this I end up viewing the site for the first time several minutes after clicking on it only to find that I had been waiting for nothing.
Right, I'm in a position such as yours every now and then. Now I understand that you meant that you can't possibly know you have to force the images to load because you have not looked at the tab yet.
"That's bullshit. What if my connection is slow and I want to leave the page loading whilst I do some other things."