One of the largest complaints I see in the forums is that of webmasters complaining that their image is not showing up in the Google search results.
Did you ever think that Google doesn't show your image because they don't think it is worth looking at?
A Google Webmaster Help thread has Googler, John Mueller, reiterating a statement in the authorship Google document that "good, recognizable headshot as your profile photo" is an important part of getting included in Google's search results.
John said that "it's really more than just having your face somewhere on the photo." So just having your face in a photo is not enough and you need to make sure you get a nice profile photo so your Google authorship thumbnail shows up.
Forum discussion at Google Webmaster Help.