The head of search spam at Google, Matt Cutts, has confirmed with us that Google has applied a 15% reduction in the amount of rich snippets displayed in the search results.
Matt Cutts announced at PubCon a couple months ago that this would happen, saying that the ability to have and use rich snippets may be taken away for low quality sites in the coming months. And this has indeed happened. Matt said this would likely reduce authorship by 15% to only show more authoritative authors.
Here is a screen shot of the drop in authorship being displayed according to MozCast:
Google’s Matt Cutts told us “I can confirm that this change has happened.”
This may or may not directly related to the blip we saw on December 17th, we have asked Google for further clarification on this.