It seems perhaps relevant to this discussion, to mention another concurrent thread here regarding Google's "dropping" of "authorship support" [webmasterworld.com
as someone who has watched with Google with interest, I suspect that the two things may well be related.
After all, if Google is intending expanding it's use of material / content from other people's websites via a "knowledge" "whatever" above organic SERPS, without directly sending the visitor to the website(s) from which Google has "gathered" the data / information / content..Then Google would hardly want to acknowledge the original source author with a thumbnail photo..
To do so might risk many to say that Google knows that the author is not Google..and that Google might well be considered to be in breach of copyright ( depending on one's legislation, and judge )..witness how Image search now "works"..each image presented by Google ( on a Google page ) says "may be subject to copyright" ( if they come from a third party website the copyright is certainly not Google's, nor is showing an entire image "fair use" ), almost all images are subject to copyright, except those marked expressly "not copyright" by the original author(s), or similarly indicated "copyright free"..Google can argue ( and have done so , IMO highly cynically ) that they cannot know that the site upon which they found the image was not the true copyright holder, hence the "may be"..By removing support for "authorship", they prepare the terrain to do the same with webmaster's written content as they have done with their images, and, given that blocking Google from content via robots.txt only prevents them taking it "directly", and does not prevent them "aquiring" content via other sites who have copy and pasted, screen shotted, pinned etc .."opting out" via robots.txt is not effective against "may be copyright"..
If, as blend27 puts forward, Google decide to put ads around either the text in their knowledge graph / vault
"results"..( currently they do put ads very close to their "knowledge graph" "insert", I'm expecting them to add ads to their image search interstitial results pages in image search, in countries where they can get away with it soon, if they do, will they only do so with images that originate from copyright holders from those countries I wonder ? )..how would ( does ) someone living elsewhere know what Google ( or any other SE for that matter ) is doing with their copyright material ?
To bear in mind...if Google was able to use your content ( images or text etc in such as blend27 posits ) would they need to keep adsense going ? after all, if they are going to do things ( with accompanying ads ) which would drastically reduce your SE traffic, why would they place adsense on sites that they were "accidentally" starving of visitors..
It could be like a death from a thousand paper cuts
Or perhaps like "slowly boiling frogs"..some of us have been saying for a long time now, that Google in particular, but also Bing, Facebook, pinterest et al were "heating the water"..
The final sound a boiled frog hears may well be Google*
*Other search engines etc are trying to do the same, but Google is more "onomatopoeic" in this context..
I suspect that within 5 years, if you have an "informational" site, the SE's will be using your content ( via "knowledge vault" or similar ) and not sending you the visitor / traffic..and if you have a commercial site the SE's will require you to buy adspace to be anywhere in their results.."organic results" as we now think of them , will have disappeared, as will adsense for all but a very reduced number of sites..