So I've been learning how to control the thumbnails that show up when a page is shared on Failbook, and I thought I'd test out how Active Social handled it.
Facebook, and a number of other sites, will respect one of two tags in the html header:
<meta content="path-to-image" property="og:image"><link rel="image_src" type="image/png" href="path-to-image">
The first being the opengraph standard, and the newer implementation.
Looks like Active Social just retrieves the page and scans for img tags it can handle. Nothing wrong with that, but controlling the thumbnails is a desirable behaviour, so it'd be great to see this included in a future version.