It is not uncommon these days to (1) see author pictures in Google search results and (2) to see them when the author and publisher did not set anything up specific for them to show up. By that I mean, they didn't do the necessary work to set up authorship on the site.
Two examples recently came up.
(1) A WebmasterWorld thread by sunnyujjawal said Pinterest URLs are showing author pictures via Google+ without the Google Authorship markup on the page.
For example, search for [pinterest arpingajjar123 and you will see this:
Now, if you look at the rich snippet data you will see it shows a Twitter account is linked. But not the Google+ account. So how does Google know? The Google+ about page for this user has this Twitter account linked in the profile and also has the Pinterest account linked. So that association is there for Google to make the assumption that the author is the same.
(2) Bas Van Den Beld on State of the Search found a story on his site showing an author profile Kristjan Mar Hauksson where his Google+ profile doesn't have any details about this user's contributions to Google+. What it does have is linkage data to his blog and Twitter account, @optimizeyourweb and because the title of the blog post has the Twitter account and author name, Google is confident to link and use the image of the Google+ profile fo that user.
Here is a picture:
So there you have it, just more proof, Google is going above and beyond to not require authors to do anything to link up content to their Google profile.
Of course with this, there may be room to trick Google into thinking the author is someone else. And I've seen cases of that.
Forum discussion at WebmasterWorld.