I'll start off by saying that this is not the Stacked team's fault.

Instead this is an issue created by a special scenario. When sharing a link to an external page of mine (I own the content, but not the site) the first 7 thumbnails are blank. Here's a screen shot to give you an idea of what I'm talking about:
The 8th image and beyond display just fine. You can test this yourself using the following link in ES:
http://www.summitpost.org/going-for-the-gusto-a-two-day-climb-on-the-torment-forbidden-traverse/875849
This is due to some sort of pagespeed that is being applied to the images themselves that do not use proper image paths. Here is a sample of one of the first 7 invalid images:
<img src='data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAkAAAAJCAAAAADF+lnMAAAAAnRSTlMA/1uRIrUAAAAYSURBVAjXY/gPAwyorA4MVgcI4JTFMAUAc51MgSsWyGIAAAAASUVORK5CYII=' pagespeed_url_hash="4028611926" onload="pagespeed.CriticalImages.checkImageForCriticality(this);">
So what we need is for a way to exclude images like this. Either parse out invalid images or check the other attributes in these cases.