Yes, I notoced this today. I assumed the pics being displayed were Rich Snippets but no, they are just pictures from the web page being reported.
I have Rich Snippets being displayed in the normal Google SERPS so I checked this out. It seems that Google are displaying a picture in Adsense for Search only for those pages which have Rich Snippets on. But the picture is different to that declared in the Rich Snippets (only one allowed for Rich Snippets). I'll check this out in more detail.
It's almost as if Google are dipping a toe in the water to see what reaction they get if they display pictures from a site in Adsense for Search which the owner has not given them permission to display. Maybe they think that if the reaction is zilch then they can then try it in the SERPS? Just a thought.
What scares me about this, if the above is true, is that I recently posted that we, as webmasters, were in control of Rich Snippets. By this I meant if we didn't declare content to Rich Snippets then Google couldn't use it. The effect of this is that Google (and Bing for that matter) would never be sure that the information they harvested by Rich Snippets was complete or even true.
But by publishing pics, even in Adsense for Content, from our sites that we have not given them permission to publish then I seem to have seriously underestimated the lengths to which Google would go.
Time for a rethink, a serious rethink.