I came across an excellent article by Cyrus Shepard on moz.com (click here), that really hit home, only because the same frustrations and information that he shares in his article is nearly identical to what I had experienced.
What I am talking about makes reference to Google Authorship, which is the displaying of your Google+ profile image within search results for posts or information that you have authored.
Cyrus’s article is excellent, and really explains how authorship can increase your traffic, simply by adding a decent image.
Keep in mind, that when an image comes up under whatever the search term is, you should be displaying a professional image as people are looking for a “credible” source.
I would also recommend keeping with a profile picture. Like Cyrus, I had tried to do some experimenting, which did not have good results. The experiment was changing my profile picture (keyword, PROFILE), to a corporate image. I do not know for sure, however I suspect that Google might have some type of photo recognition software that recognizes a true portrait as opposed to “something else”. The results were our images did change almost immediately, but then were dropped completely.
Anyway, the information and tips from Cyrus are excellent, have a read by clicking here.