A Google Webmaster Help thread has one webmaster complaining that his author icon is not showing up in the search results. To be honest, this is a common complaint.
Pierre Far responded to this case explaining why his author icon may not be displaying in this case.
One reason we covered already. It is that your headshot must be recognizable and not some sort of abstract icon. This webmaster had this issue.
The second reason we did not cover. The "Contributor To" section of your Google+ profile must have the proper URLs of the sites you contribute to. For example, in this case, the user listed the non www version of his site and Pierre said he had to have the www version of the site for it to work in this case.
Pierre Far from Google wrote:
In the profile annotated as the author ( https://plus.google.com/u/0/111928490582871469703/about ) you specify you are a contributor to different URLs on gryffynsaeyrieborzoi.com but your website is www.gryffynsaeyrieborzoi.com. You should specify you are a contributor to the www variant.
Forum discussion at Google Webmaster Help.