It should work the same with JPEGs and GIFs. As far as hotlinking goes, well, it depends on the site I guess. Some webmasters don't like it if you hotlink an image that was uploaded to their site, and set their server to block it. Most will probably never even notice it, though. And if it's already on an image-sharing site like Imgur or Tumblr, it's fine.
I use Imgur a lot (including for that pic), so what I often do is add site:imgur.com to a Google Image Search so that it only shows me pictures from that site. (So the full search would be "I understood that reference site:imgur.com").