In the past I had been heavily impacted by hotlink spam sites linking to my content, but I managed to effectively block it. Yeah! At the same time my rankings went up. Today, as a result of the update, my rankings went down. Correlation is not causation, but still I figured, I should take a look in detail at some of the search results for my site. And sure enough the hotlinking is back. But not like before. My blocking remains effective.
The spammers are now using Google images, that is they link to your image and using Javascript, "onerror" fallback on a Google image search url of the image. So if you block them, that's ok they will steal from Google.
I'm not sure how truly effective the technique is, a few of the links I checked were not working in either instance, but some where.
How the heck are you supposed to fight that?